errors: add GIT_EEOF to indicate early EOF

This can be used by tools to show mesages about failing to communicate
with the server. The error message in this case will often contain the
server's error message, as far as it managed to send anything.

CHANGELOG.md

@@ -93,6 +93,11 @@ support for HTTPS connections insead of OpenSSL.
 * `git_stash_pop()` will apply a stashed state (like `git_stash_apply()`)
   but will remove the stashed state after a successful application.
 
+* A new error code `GIT_EEOF` indicates an early EOF from the
+  server. This typically indicates an error with the URL or
+  configuration of the server, and tools can use this to show messages
+  about failing to communicate with the server.
+
 ### API removals
 
 * `git_remote_save()` and `git_remote_clear_refspecs()` has been

include/git2/errors.h

@@ -45,6 +45,7 @@ typedef enum {
 	GIT_ECERTIFICATE    = -17,      /**< Server certificate is invalid */
 	GIT_EAPPLIED        = -18,	/**< Patch/merge has already been applied */
 	GIT_EPEEL           = -19,      /**< The requested peel operation is not possible */
+	GIT_EEOF            = -20,      /**< Unexpected EOF */
 
 	GIT_PASSTHROUGH     = -30,	/**< Internal only */
 	GIT_ITEROVER        = -31,	/**< Signals end of iteration with iterator */

src/openssl_stream.c

@@ -55,6 +55,7 @@ static int ssl_set_error(SSL *ssl, int error)
 			break;
 		}
 		giterr_set(GITERR_NET, "SSL error: received early EOF");
+		return GIT_EEOF;
 		break;
 	case SSL_ERROR_SSL:
 		e = ERR_get_error();

src/transports/smart_protocol.c

@@ -52,7 +52,7 @@ int git_smart__store_refs(transport_smart *t, int flushes)
 
 			if (recvd == 0 && !flush) {
 				giterr_set(GITERR_NET, "early EOF");
-				return -1;
+				return GIT_EEOF;
 			}
 
 			continue;
@@ -770,7 +770,7 @@ static int parse_report(transport_smart *transport, git_push *push)
 
 			if (recvd == 0) {
 				giterr_set(GITERR_NET, "early EOF");
-				return -1;
+				return GIT_EEOF;
 			}
 			continue;
 		}

src/transports/ssh.c

@@ -129,10 +129,14 @@ static int ssh_stream_read(
 		return -1;
 	}
 
-	/* Having something in stderr is typically a not-found error */
+	/*
+	 * If we can't get anything out of stdout, it's typically a
+	 * not-found error, so read from stderr and signal EOF on
+	 * stderr.
+	 */
 	if (rc == 0 && (rc = libssh2_channel_read_stderr(s->channel, buffer, buf_size)) > 0) {
 		giterr_set(GITERR_SSH, "%*s", rc, buffer);
-		return -1;
+		return GIT_EEOF;
 	}