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Add rudimentary error checks and reformat comments

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There were a number of functions assigning their return value to
`error` without much explanation.  I added in some rudimentary
error checking to help flesh out the example.

Also, I reformatted all of the comments down to 80 cols (and in
some cases, slightly updated the wording).
This commit is contained in:
Russell Belfer 2013-02-15 15:58:13 -08:00
parent 1d75acf7b7
commit a7ed746093
1 changed files with 205 additions and 144 deletions
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349
examples/general.c
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@ -1,19 +1,20 @@
// [**libgit2**][lg] is a portable, pure C implementation of the Git core methods
// provided as a re-entrant linkable library with a solid API, allowing you
// to write native speed custom Git applications in any language which
// supports C bindings.
// [**libgit2**][lg] is a portable, pure C implementation of the Git core
// methods provided as a re-entrant linkable library with a solid API,
// allowing you to write native speed custom Git applications in any
// language which supports C bindings.
//
// This file is an example of using that API in a real, compilable C file.
// As the API is updated, this file will be updated to demonstrate the
// new functionality.
// As the API is updated, this file will be updated to demonstrate the new
// functionality.
//
// If you're trying to write something in C using [libgit2][lg], you will also want
// to check out the generated [API documentation][ap]. We've
// tried to link to the relevant sections of the API docs in each section in this file.
// If you're trying to write something in C using [libgit2][lg], you should
// also check out the generated [API documentation][ap]. We try to link to
// the relevant sections of the API docs in each section in this file.
//
// **libgit2** only implements the core plumbing functions, not really the higher
// level porcelain stuff. For a primer on Git Internals that you will need to know
// to work with Git at this level, check out [Chapter 9][pg] of the Pro Git book.
// **libgit2** (for the most part) only implements the core plumbing
// functions, not really the higher level porcelain stuff. For a primer on
// Git Internals that you will need to know to work with Git at this level,
// check out [Chapter 9][pg] of the Pro Git book.
//
// [lg]: http://libgit2.github.com
// [ap]: http://libgit2.github.com/libgit2
@ -21,43 +22,63 @@
// ### Includes
// Including the `git2.h` header will include all the other libgit2 headers that you need.
// It should be the only thing you need to include in order to compile properly and get
// all the libgit2 API.
// Including the `git2.h` header will include all the other libgit2 headers
// that you need. It should be the only thing you need to include in order
// to compile properly and get all the libgit2 API.
#include <git2.h>
#include <stdio.h>
// Almost all libgit2 functions return 0 on success or negative on error.
// This is not production quality error checking, but should be sufficient
// as an example.
static void check_error(int error_code, const char *action)
{
if (!error_code)
return;
const git_error *error = giterr_last();
printf("Error %d %s - %s\n", error_code, action,
(error && error->message) ? error->message : "???");
exit(1);
}
int main (int argc, char** argv)
{
// ### Opening the Repository
// There are a couple of methods for opening a repository, this being the simplest.
// There are also [methods][me] for specifying the index file and work tree locations, here
// we are assuming they are in the normal places.
// There are a couple of methods for opening a repository, this being the
// simplest. There are also [methods][me] for specifying the index file
// and work tree locations, here we assume they are in the normal places.
//
// [me]: http://libgit2.github.com/libgit2/#HEAD/group/repository
int error;
const char *repo_path = (argc > 1) ? argv[1] : "/opt/libgit2-test/.git";
git_repository *repo;
if (argc > 1) {
git_repository_open(&repo, argv[1]);
} else {
git_repository_open(&repo, "/opt/libgit2-test/.git");
}
error = git_repository_open(&repo, repo_path);
check_error(error, "opening repository");
// ### SHA-1 Value Conversions
// For our first example, we will convert a 40 character hex value to the 20 byte raw SHA1 value.
// For our first example, we will convert a 40 character hex value to the
// 20 byte raw SHA1 value.
printf("*Hex to Raw*\n");
char hex[] = "fd6e612585290339ea8bf39c692a7ff6a29cb7c3";
// The `git_oid` is the structure that keeps the SHA value. We will use this throughout the example
// for storing the value of the current SHA key we're working with.
// The `git_oid` is the structure that keeps the SHA value. We will use
// this throughout the example for storing the value of the current SHA
// key we're working with.
git_oid oid;
git_oid_fromstr(&oid, hex);
// Once we've converted the string into the oid value, we can get the raw value of the SHA.
// Once we've converted the string into the oid value, we can get the raw
// value of the SHA.
printf("Raw 20 bytes: [%.20s]\n", (&oid)->id);
// Next we will convert the 20 byte raw SHA1 value to a human readable 40 char hex value.
// Next we will convert the 20 byte raw SHA1 value to a human readable 40
// char hex value.
printf("\n*Raw to Hex*\n");
char out[41];
out[40] = '\0';
@ -67,10 +88,12 @@ int main (int argc, char** argv)
printf("SHA hex string: %s\n", out);
// ### Working with the Object Database
// **libgit2** provides [direct access][odb] to the object database.
// The object database is where the actual objects are stored in Git. For
// **libgit2** provides [direct access][odb] to the object database. The
// object database is where the actual objects are stored in Git. For
// working with raw objects, we'll need to get this structure from the
// repository.
//
// [odb]: http://libgit2.github.com/libgit2/#HEAD/group/odb
git_odb *odb;
git_repository_odb(&odb, repo);
@ -82,55 +105,60 @@ int main (int argc, char** argv)
git_otype otype;
const unsigned char *data;
const char *str_type;
int error;
// We can read raw objects directly from the object database if we have the oid (SHA)
// of the object. This allows us to access objects without knowing thier type and inspect
// the raw bytes unparsed.
// We can read raw objects directly from the object database if we have
// the oid (SHA) of the object. This allows us to access objects without
// knowing thier type and inspect the raw bytes unparsed.
error = git_odb_read(&obj, odb, &oid);
check_error(error, "finding object in repository");
// A raw object only has three properties - the type (commit, blob, tree or tag), the size
// of the raw data and the raw, unparsed data itself. For a commit or tag, that raw data
// is human readable plain ASCII text. For a blob it is just file contents, so it could be
// text or binary data. For a tree it is a special binary format, so it's unlikely to be
// hugely helpful as a raw object.
// A raw object only has three properties - the type (commit, blob, tree
// or tag), the size of the raw data and the raw, unparsed data itself.
// For a commit or tag, that raw data is human readable plain ASCII
// text. For a blob it is just file contents, so it could be text or
// binary data. For a tree it is a special binary format, so it's unlikely
// to be hugely helpful as a raw object.
data = (const unsigned char *)git_odb_object_data(obj);
otype = git_odb_object_type(obj);
// We provide methods to convert from the object type which is an enum, to a string
// representation of that value (and vice-versa).
// We provide methods to convert from the object type which is an enum, to
// a string representation of that value (and vice-versa).
str_type = git_object_type2string(otype);
printf("object length and type: %d, %s\n",
(int)git_odb_object_size(obj),
str_type);
// For proper memory management, close the object when you are done with it or it will leak
// memory.
// For proper memory management, close the object when you are done with
// it or it will leak memory.
git_odb_object_free(obj);
// #### Raw Object Writing
printf("\n*Raw Object Write*\n");
// You can also write raw object data to Git. This is pretty cool because it gives you
// direct access to the key/value properties of Git. Here we'll write a new blob object
// that just contains a simple string. Notice that we have to specify the object type as
// the `git_otype` enum.
// You can also write raw object data to Git. This is pretty cool because
// it gives you direct access to the key/value properties of Git. Here
// we'll write a new blob object that just contains a simple string.
// Notice that we have to specify the object type as the `git_otype` enum.
git_odb_write(&oid, odb, "test data", sizeof("test data") - 1, GIT_OBJ_BLOB);
// Now that we've written the object, we can check out what SHA1 was generated when the
// object was written to our database.
// Now that we've written the object, we can check out what SHA1 was
// generated when the object was written to our database.
git_oid_fmt(out, &oid);
printf("Written Object: %s\n", out);
// ### Object Parsing
// libgit2 has methods to parse every object type in Git so you don't have to work directly
// with the raw data. This is much faster and simpler than trying to deal with the raw data
// yourself.
// libgit2 has methods to parse every object type in Git so you don't have
// to work directly with the raw data. This is much faster and simpler
// than trying to deal with the raw data yourself.
// #### Commit Parsing
// [Parsing commit objects][pco] is simple and gives you access to all the data in the commit
// - the // author (name, email, datetime), committer (same), tree, message, encoding and parent(s).
// [Parsing commit objects][pco] is simple and gives you access to all the
// data in the commit - the author (name, email, datetime), committer
// (same), tree, message, encoding and parent(s).
//
// [pco]: http://libgit2.github.com/libgit2/#HEAD/group/commit
printf("\n*Commit Parsing*\n");
@ -139,27 +167,31 @@ int main (int argc, char** argv)
git_oid_fromstr(&oid, "f0877d0b841d75172ec404fc9370173dfffc20d1");
error = git_commit_lookup(&commit, repo, &oid);
check_error(error, "looking up commit");
const git_signature *author, *cmtter;
const char *message;
time_t ctime;
unsigned int parents, p;
// Each of the properties of the commit object are accessible via methods, including commonly
// needed variations, such as `git_commit_time` which returns the author time and `_message`
// which gives you the commit message.
// Each of the properties of the commit object are accessible via methods,
// including commonly needed variations, such as `git_commit_time` which
// returns the author time and `git_commit_message` which gives you the
// commit message (as a NUL-terminated string).
message = git_commit_message(commit);
author = git_commit_author(commit);
cmtter = git_commit_committer(commit);
ctime = git_commit_time(commit);
// The author and committer methods return [git_signature] structures, which give you name, email
// and `when`, which is a `git_time` structure, giving you a timestamp and timezone offset.
// The author and committer methods return [git_signature] structures,
// which give you name, email and `when`, which is a `git_time` structure,
// giving you a timestamp and timezone offset.
printf("Author: %s (%s)\n", author->name, author->email);
// Commits can have zero or more parents. The first (root) commit will have no parents, most commits
// will have one, which is the commit it was based on, and merge commits will have two or more.
// Commits can technically have any number, though it's pretty rare to have more than two.
// Commits can have zero or more parents. The first (root) commit will
// have no parents, most commits will have one (i.e. the commit it was
// based on) and merge commits will have two or more. Commits can
// technically have any number, though it's rare to have more than two.
parents = git_commit_parentcount(commit);
for (p = 0;p < parents;p++) {
git_commit *parent;
@ -169,15 +201,17 @@ int main (int argc, char** argv)
git_commit_free(parent);
}
// Don't forget to close the object to prevent memory leaks. You will have to do this for
// all the objects you open and parse.
// Don't forget to close the object to prevent memory leaks. You will have
// to do this for all the objects you open and parse.
git_commit_free(commit);
// #### Writing Commits
// libgit2 provides a couple of methods to create commit objects easily as
// well. There are four different create signatures, we'll just show one
// of them here. You can read about the other ones in the [commit API
// docs][cd].
//
// libgit2 provides a couple of methods to create commit objects easily as well. There are four
// different create signatures, we'll just show one of them here. You can read about the other
// ones in the [commit API docs][cd].
// [cd]: http://libgit2.github.com/libgit2/#HEAD/group/commit
printf("\n*Commit Writing*\n");
@ -185,24 +219,27 @@ int main (int argc, char** argv)
git_tree *tree;
git_commit *parent;
// Creating signatures for an authoring identity and time is pretty simple - you will need to have
// this to create a commit in order to specify who created it and when. Default values for the name
// and email should be found in the `user.name` and `user.email` configuration options. See the `config`
// section of this example file to see how to access config values.
git_signature_new((git_signature **)&author, "Scott Chacon", "schacon@gmail.com",
123456789, 60);
git_signature_new((git_signature **)&cmtter, "Scott A Chacon", "scott@github.com",
987654321, 90);
// Creating signatures for an authoring identity and time is simple. You
// will need to do this to specify who created a commit and when. Default
// values for the name and email should be found in the `user.name` and
// `user.email` configuration options. See the `config` section of this
// example file to see how to access config values.
git_signature_new((git_signature **)&author,
"Scott Chacon", "schacon@gmail.com", 123456789, 60);
git_signature_new((git_signature **)&cmtter,
"Scott A Chacon", "scott@github.com", 987654321, 90);
// Commit objects need a tree to point to and optionally one or more parents. Here we're creating oid
// objects to create the commit with, but you can also use
// Commit objects need a tree to point to and optionally one or more
// parents. Here we're creating oid objects to create the commit with,
// but you can also use
git_oid_fromstr(&tree_id, "28873d96b4e8f4e33ea30f4c682fd325f7ba56ac");
git_tree_lookup(&tree, repo, &tree_id);
git_oid_fromstr(&parent_id, "f0877d0b841d75172ec404fc9370173dfffc20d1");
git_commit_lookup(&parent, repo, &parent_id);
// Here we actually create the commit object with a single call with all the values we need to create
// the commit. The SHA key is written to the `commit_id` variable here.
// Here we actually create the commit object with a single call with all
// the values we need to create the commit. The SHA key is written to the
// `commit_id` variable here.
git_commit_create_v(
&commit_id, /* out id */
repo,
@ -219,35 +256,42 @@ int main (int argc, char** argv)
printf("New Commit: %s\n", out);
// #### Tag Parsing
// You can parse and create tags with the [tag management API][tm], which functions very similarly
// to the commit lookup, parsing and creation methods, since the objects themselves are very similar.
// You can parse and create tags with the [tag management API][tm], which
// functions very similarly to the commit lookup, parsing and creation
// methods, since the objects themselves are very similar.
//
// [tm]: http://libgit2.github.com/libgit2/#HEAD/group/tag
printf("\n*Tag Parsing*\n");
git_tag *tag;
const char *tmessage, *tname;
git_otype ttype;
// We create an oid for the tag object if we know the SHA and look it up in the repository the same
// way that we would a commit (or any other) object.
// We create an oid for the tag object if we know the SHA and look it up
// the same way that we would a commit (or any other object).
git_oid_fromstr(&oid, "bc422d45275aca289c51d79830b45cecebff7c3a");
error = git_tag_lookup(&tag, repo, &oid);
check_error(error, "looking up tag");
// Now that we have the tag object, we can extract the information it generally contains: the target
// (usually a commit object), the type of the target object (usually 'commit'), the name ('v1.0'),
// the tagger (a git_signature - name, email, timestamp), and the tag message.
// Now that we have the tag object, we can extract the information it
// generally contains: the target (usually a commit object), the type of
// the target object (usually 'commit'), the name ('v1.0'), the tagger (a
// git_signature - name, email, timestamp), and the tag message.
git_tag_target((git_object **)&commit, tag);
tname = git_tag_name(tag); // "test"
ttype = git_tag_target_type(tag); // GIT_OBJ_COMMIT (otype enum)
tmessage = git_tag_message(tag); // "tag message\n"
tname = git_tag_name(tag); // "test"
ttype = git_tag_target_type(tag); // GIT_OBJ_COMMIT (otype enum)
tmessage = git_tag_message(tag); // "tag message\n"
printf("Tag Message: %s\n", tmessage);
git_commit_free(commit);
// #### Tree Parsing
// [Tree parsing][tp] is a bit different than the other objects, in that we have a subtype which is the
// tree entry. This is not an actual object type in Git, but a useful structure for parsing and
// traversing tree entries.
// [Tree parsing][tp] is a bit different than the other objects, in that
// we have a subtype which is the tree entry. This is not an actual
// object type in Git, but a useful structure for parsing and traversing
// tree entries.
//
// [tp]: http://libgit2.github.com/libgit2/#HEAD/group/tree
printf("\n*Tree Parsing*\n");
@ -259,31 +303,36 @@ int main (int argc, char** argv)
git_oid_fromstr(&oid, "2a741c18ac5ff082a7caaec6e74db3075a1906b5");
git_tree_lookup(&tree, repo, &oid);
// Getting the count of entries in the tree so you can iterate over them if you want to.
// Getting the count of entries in the tree so you can iterate over them
// if you want to.
size_t cnt = git_tree_entrycount(tree); // 3
printf("tree entries: %d\n", (int)cnt);
entry = git_tree_entry_byindex(tree, 0);
printf("Entry name: %s\n", git_tree_entry_name(entry)); // "hello.c"
// You can also access tree entries by name if you know the name of the entry you're looking for.
// You can also access tree entries by name if you know the name of the
// entry you're looking for.
entry = git_tree_entry_byname(tree, "hello.c");
git_tree_entry_name(entry); // "hello.c"
// Once you have the entry object, you can access the content or subtree (or commit, in the case
// of submodules) that it points to. You can also get the mode if you want.
// Once you have the entry object, you can access the content or subtree
// (or commit, in the case of submodules) that it points to. You can also
// get the mode if you want.
git_tree_entry_to_object(&objt, repo, entry); // blob
// Remember to close the looked-up object once you are done using it
git_object_free(objt);
// #### Blob Parsing
//
// The last object type is the simplest and requires the least parsing help. Blobs are just file
// contents and can contain anything, there is no structure to it. The main advantage to using the
// [simple blob api][ba] is that when you're creating blobs you don't have to calculate the size
// of the content. There is also a helper for reading a file from disk and writing it to the db and
// getting the oid back so you don't have to do all those steps yourself.
// The last object type is the simplest and requires the least parsing
// help. Blobs are just file contents and can contain anything, there is
// no structure to it. The main advantage to using the [simple blob
// api][ba] is that when you're creating blobs you don't have to calculate
// the size of the content. There is also a helper for reading a file
// from disk and writing it to the db and getting the oid back so you
// don't have to do all those steps yourself.
//
// [ba]: http://libgit2.github.com/libgit2/#HEAD/group/blob
@ -294,19 +343,21 @@ int main (int argc, char** argv)
git_blob_lookup(&blob, repo, &oid);
// You can access a buffer with the raw contents of the blob directly.
// Note that this buffer may not be contain ASCII data for certain blobs (e.g. binary files):
// do not consider the buffer a NULL-terminated string, and use the `git_blob_rawsize` attribute to
// find out its exact size in bytes
// Note that this buffer may not be contain ASCII data for certain blobs
// (e.g. binary files): do not consider the buffer a NULL-terminated
// string, and use the `git_blob_rawsize` attribute to find out its exact
// size in bytes
printf("Blob Size: %ld\n", (long)git_blob_rawsize(blob)); // 8
git_blob_rawcontent(blob); // "content"
// ### Revwalking
//
// The libgit2 [revision walking api][rw] provides methods to traverse the directed graph created
// by the parent pointers of the commit objects. Since all commits point back to the commit that
// came directly before them, you can walk this parentage as a graph and find all the commits that
// were ancestors of (reachable from) a given starting point. This can allow you to create `git log`
// type functionality.
// The libgit2 [revision walking api][rw] provides methods to traverse the
// directed graph created by the parent pointers of the commit objects.
// Since all commits point back to the commit that came directly before
// them, you can walk this parentage as a graph and find all the commits
// that were ancestors of (reachable from) a given starting point. This
// can allow you to create `git log` type functionality.
//
// [rw]: http://libgit2.github.com/libgit2/#HEAD/group/revwalk
@ -316,11 +367,13 @@ int main (int argc, char** argv)
git_oid_fromstr(&oid, "f0877d0b841d75172ec404fc9370173dfffc20d1");
// To use the revwalker, create a new walker, tell it how you want to sort the output and then push
// one or more starting points onto the walker. If you want to emulate the output of `git log` you
// would push the SHA of the commit that HEAD points to into the walker and then start traversing them.
// You can also 'hide' commits that you want to stop at or not see any of their ancestors. So if you
// want to emulate `git log branch1..branch2`, you would push the oid of `branch2` and hide the oid
// To use the revwalker, create a new walker, tell it how you want to sort
// the output and then push one or more starting points onto the walker.
// If you want to emulate the output of `git log` you would push the SHA
// of the commit that HEAD points to into the walker and then start
// traversing them. You can also 'hide' commits that you want to stop at
// or not see any of their ancestors. So if you want to emulate `git log
// branch1..branch2`, you would push the oid of `branch2` and hide the oid
// of `branch1`.
git_revwalk_new(&walk, repo);
git_revwalk_sorting(walk, GIT_SORT_TOPOLOGICAL | GIT_SORT_REVERSE);
@ -329,28 +382,32 @@ int main (int argc, char** argv)
const git_signature *cauth;
const char *cmsg;
// Now that we have the starting point pushed onto the walker, we can start asking for ancestors. It
// will return them in the sorting order we asked for as commit oids.
// We can then lookup and parse the commited pointed at by the returned OID;
// note that this operation is specially fast since the raw contents of the commit object will
// be cached in memory
// Now that we have the starting point pushed onto the walker, we start
// asking for ancestors. It will return them in the sorting order we asked
// for as commit oids. We can then lookup and parse the commited pointed
// at by the returned OID; note that this operation is specially fast
// since the raw contents of the commit object will be cached in memory
while ((git_revwalk_next(&oid, walk)) == 0) {
error = git_commit_lookup(&wcommit, repo, &oid);
check_error(error, "looking up commit during revwalk");
cmsg = git_commit_message(wcommit);
cauth = git_commit_author(wcommit);
printf("%s (%s)\n", cmsg, cauth->email);
git_commit_free(wcommit);
}
// Like the other objects, be sure to free the revwalker when you're done to prevent memory leaks.
// Also, make sure that the repository being walked it not deallocated while the walk is in
// progress, or it will result in undefined behavior
// Like the other objects, be sure to free the revwalker when you're done
// to prevent memory leaks. Also, make sure that the repository being
// walked it not deallocated while the walk is in progress, or it will
// result in undefined behavior
git_revwalk_free(walk);
// ### Index File Manipulation
//
// The [index file API][gi] allows you to read, traverse, update and write the Git index file
// (sometimes thought of as the staging area).
// The [index file API][gi] allows you to read, traverse, update and write
// the Git index file (sometimes thought of as the staging area).
//
// [gi]: http://libgit2.github.com/libgit2/#HEAD/group/index
@ -359,15 +416,18 @@ int main (int argc, char** argv)
git_index *index;
unsigned int i, ecount;
// You can either open the index from the standard location in an open repository, as we're doing
// here, or you can open and manipulate any index file with `git_index_open_bare()`. The index
// for the repository will be located and loaded from disk.
// You can either open the index from the standard location in an open
// repository, as we're doing here, or you can open and manipulate any
// index file with `git_index_open_bare()`. The index for the repository
// will be located and loaded from disk.
git_repository_index(&index, repo);
// For each entry in the index, you can get a bunch of information including the SHA (oid), path
// and mode which map to the tree objects that are written out. It also has filesystem properties
// to help determine what to inspect for changes (ctime, mtime, dev, ino, uid, gid, file_size and flags)
// All these properties are exported publicly in the `git_index_entry` struct
// For each entry in the index, you can get a bunch of information
// including the SHA (oid), path and mode which map to the tree objects
// that are written out. It also has filesystem properties to help
// determine what to inspect for changes (ctime, mtime, dev, ino, uid,
// gid, file_size and flags) All these properties are exported publicly in
// the `git_index_entry` struct
ecount = git_index_entrycount(index);
for (i = 0; i < ecount; ++i) {
const git_index_entry *e = git_index_get_byindex(index, i);
@ -380,24 +440,25 @@ int main (int argc, char** argv)
git_index_free(index);
// ### References
//
// The [reference API][ref] allows you to list, resolve, create and update references such as
// branches, tags and remote references (everything in the .git/refs directory).
// The [reference API][ref] allows you to list, resolve, create and update
// references such as branches, tags and remote references (everything in
// the .git/refs directory).
//
// [ref]: http://libgit2.github.com/libgit2/#HEAD/group/reference
printf("\n*Reference Listing*\n");
// Here we will implement something like `git for-each-ref` simply listing out all available
// references and the object SHA they resolve to.
// Here we will implement something like `git for-each-ref` simply listing
// out all available references and the object SHA they resolve to.
git_strarray ref_list;
git_reference_list(&ref_list, repo, GIT_REF_LISTALL);
const char *refname;
git_reference *ref;
// Now that we have the list of reference names, we can lookup each ref one at a time and
// resolve them to the SHA, then print both values out.
// Now that we have the list of reference names, we can lookup each ref
// one at a time and resolve them to the SHA, then print both values out.
for (i = 0; i < ref_list.count; ++i) {
refname = ref_list.strings[i];
git_reference_lookup(&ref, repo, refname);
@ -420,9 +481,9 @@ int main (int argc, char** argv)
git_strarray_free(&ref_list);
// ### Config Files
//
// The [config API][config] allows you to list and updatee config values in
// any of the accessible config file locations (system, global, local).
// The [config API][config] allows you to list and updatee config values
// in any of the accessible config file locations (system, global, local).
//
// [config]: http://libgit2.github.com/libgit2/#HEAD/group/config