Split GPG interface into its own helper library

gitster · gitster · commit 2f47eae2a133 · 2011-11-04T21:40:25.000-07:00
This mostly moves existing code from builtin/tag.c (for signing)
and builtin/verify-tag.c (for verifying) to a new gpg-interface.c
file to provide a more generic library interface.

 - sign_buffer() takes a payload strbuf, a signature strbuf, and a signing
   key, runs "gpg" to produce a detached signature for the payload, and
   appends it to the signature strbuf. The contents of a signed tag that
   concatenates the payload and the detached signature can be produced by
   giving the same strbuf as payload and signature strbuf.

 - verify_signed_buffer() takes a payload and a detached signature as
   &lt;ptr, len&gt; pairs, and runs "gpg --verify" to see if the payload matches
   the signature. It can optionally capture the output from GPG to allow
   the callers to pretty-print it in a way more suitable for their
   contexts.

"verify-tag" (aka "tag -v") used to save the whole tag contents as if it
is a detached signature, and fed gpg the payload part of the tag. It
relied on gpg to fail when the given tag is not signed but just is
annotated.  The updated run_gpg_verify() function detects the lack of
detached signature in the input, and errors out without bothering "gpg".

Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/Makefile b/Makefile
@@ -528,6 +528,7 @@ LIB_H += exec_cmd.h
 LIB_H += fsck.h
 LIB_H += gettext.h
 LIB_H += git-compat-util.h
+LIB_H += gpg-interface.h
 LIB_H += graph.h
 LIB_H += grep.h
 LIB_H += hash.h
@@ -621,6 +622,7 @@ LIB_OBJS += entry.o
 LIB_OBJS += environment.o
 LIB_OBJS += exec_cmd.o
 LIB_OBJS += fsck.o
+LIB_OBJS += gpg-interface.o
 LIB_OBJS += graph.o
 LIB_OBJS += grep.o
 LIB_OBJS += hash.o
diff --git a/builtin/tag.c b/builtin/tag.c
@@ -14,6 +14,7 @@
 #include "parse-options.h"
 #include "diff.h"
 #include "revision.h"
+#include "gpg-interface.h"
 
 static const char * const git_tag_usage[] = {
 	"git tag [-a|-s|-u <key-id>] [-f] [-m <msg>|-F <file>] <tagname> [<head>]",
@@ -23,8 +24,6 @@ static const char * const git_tag_usage[] = {
 	NULL
 };
 
-static char signingkey[1000];
-
 struct tag_filter {
 	const char **patterns;
 	int lines;
@@ -208,60 +207,7 @@ static int verify_tag(const char *name, const char *ref,
 
 static int do_sign(struct strbuf *buffer)
 {
-	struct child_process gpg;
-	const char *args[4];
-	char *bracket;
-	int len;
-	int i, j;
-
-	if (!*signingkey) {
-		if (strlcpy(signingkey, git_committer_info(IDENT_ERROR_ON_NO_NAME),
-				sizeof(signingkey)) > sizeof(signingkey) - 1)
-			return error(_("committer info too long."));
-		bracket = strchr(signingkey, '>');
-		if (bracket)
-			bracket[1] = '\0';
-	}
-
-	/* When the username signingkey is bad, program could be terminated
-	 * because gpg exits without reading and then write gets SIGPIPE. */
-	signal(SIGPIPE, SIG_IGN);
-
-	memset(&gpg, 0, sizeof(gpg));
-	gpg.argv = args;
-	gpg.in = -1;
-	gpg.out = -1;
-	args[0] = "gpg";
-	args[1] = "-bsau";
-	args[2] = signingkey;
-	args[3] = NULL;
-
-	if (start_command(&gpg))
-		return error(_("could not run gpg."));
-
-	if (write_in_full(gpg.in, buffer->buf, buffer->len) != buffer->len) {
-		close(gpg.in);
-		close(gpg.out);
-		finish_command(&gpg);
-		return error(_("gpg did not accept the tag data"));
-	}
-	close(gpg.in);
-	len = strbuf_read(buffer, gpg.out, 1024);
-	close(gpg.out);
-
-	if (finish_command(&gpg) || !len || len < 0)
-		return error(_("gpg failed to sign the tag"));
-
-	/* Strip CR from the line endings, in case we are on Windows. */
-	for (i = j = 0; i < buffer->len; i++)
-		if (buffer->buf[i] != '\r') {
-			if (i != j)
-				buffer->buf[j] = buffer->buf[i];
-			j++;
-		}
-	strbuf_setlen(buffer, j);
-
-	return 0;
+	return sign_buffer(buffer, buffer, get_signing_key());
 }
 
 static const char tag_template[] =
@@ -270,21 +216,11 @@ static const char tag_template[] =
 	"# Write a tag message\n"
 	"#\n");
 
-static void set_signingkey(const char *value)
-{
-	if (strlcpy(signingkey, value, sizeof(signingkey)) >= sizeof(signingkey))
-		die(_("signing key value too long (%.10s...)"), value);
-}
-
 static int git_tag_config(const char *var, const char *value, void *cb)
 {
-	if (!strcmp(var, "user.signingkey")) {
-		if (!value)
-			return config_error_nonbool(var);
-		set_signingkey(value);
-		return 0;
-	}
-
+	int status = git_gpg_config(var, value, cb);
+	if (status)
+		return status;
 	return git_default_config(var, value, cb);
 }
 
@@ -463,7 +399,7 @@ int cmd_tag(int argc, const char **argv, const char *prefix)
 
 	if (keyid) {
 		sign = 1;
-		set_signingkey(keyid);
+		set_signing_key(keyid);
 	}
 	if (sign)
 		annotate = 1;
diff --git a/builtin/verify-tag.c b/builtin/verify-tag.c
@@ -11,6 +11,7 @@
 #include "run-command.h"
 #include <signal.h>
 #include "parse-options.h"
+#include "gpg-interface.h"
 
 static const char * const verify_tag_usage[] = {
 		"git verify-tag [-v|--verbose] <tag>...",
@@ -19,42 +20,16 @@ static const char * const verify_tag_usage[] = {
 
 static int run_gpg_verify(const char *buf, unsigned long size, int verbose)
 {
-	struct child_process gpg;
-	const char *args_gpg[] = {"gpg", "--verify", "FILE", "-", NULL};
-	char path[PATH_MAX];
-	size_t len;
-	int fd, ret;
+	int len;
 
-	fd = git_mkstemp(path, PATH_MAX, ".git_vtag_tmpXXXXXX");
-	if (fd < 0)
-		return error("could not create temporary file '%s': %s",
-						path, strerror(errno));
-	if (write_in_full(fd, buf, size) < 0)
-		return error("failed writing temporary file '%s': %s",
-						path, strerror(errno));
-	close(fd);
-
-	/* find the length without signature */
 	len = parse_signature(buf, size);
 	if (verbose)
 		write_in_full(1, buf, len);
 
-	memset(&gpg, 0, sizeof(gpg));
-	gpg.argv = args_gpg;
-	gpg.in = -1;
-	args_gpg[2] = path;
-	if (start_command(&gpg)) {
-		unlink(path);
-		return error("could not run gpg.");
-	}
-
-	write_in_full(gpg.in, buf, len);
-	close(gpg.in);
-	ret = finish_command(&gpg);
+	if (size == len)
+		return error("no signature found");
 
-	unlink_or_warn(path);
-
-	return ret;
+	return verify_signed_buffer(buf, len, buf + len, size - len, NULL);
 }
 
 static int verify_tag(const char *name, int verbose)
diff --git a/gpg-interface.c b/gpg-interface.c
@@ -0,0 +1,138 @@
+#include "cache.h"
+#include "run-command.h"
+#include "strbuf.h"
+#include "gpg-interface.h"
+#include "sigchain.h"
+
+static char *configured_signing_key;
+
+void set_signing_key(const char *key)
+{
+	free(configured_signing_key);
+	configured_signing_key = xstrdup(key);
+}
+
+int git_gpg_config(const char *var, const char *value, void *cb)
+{
+	if (!strcmp(var, "user.signingkey")) {
+		if (!value)
+			return config_error_nonbool(var);
+		set_signing_key(value);
+	}
+	return 0;
+}
+
+const char *get_signing_key(void)
+{
+	if (configured_signing_key)
+		return configured_signing_key;
+	return git_committer_info(IDENT_ERROR_ON_NO_NAME|IDENT_NO_DATE);
+}
+
+/*
+ * Create a detached signature for the contents of "buffer" and append
+ * it after "signature"; "buffer" and "signature" can be the same
+ * strbuf instance, which would cause the detached signature appended
+ * at the end.
+ */
+int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key)
+{
+	struct child_process gpg;
+	const char *args[4];
+	ssize_t len;
+	size_t i, j, bottom;
+
+	memset(&gpg, 0, sizeof(gpg));
+	gpg.argv = args;
+	gpg.in = -1;
+	gpg.out = -1;
+	args[0] = "gpg";
+	args[1] = "-bsau";
+	args[2] = signing_key;
+	args[3] = NULL;
+
+	if (start_command(&gpg))
+		return error(_("could not run gpg."));
+
+	/*
+	 * When the username signingkey is bad, program could be terminated
+	 * because gpg exits without reading and then write gets SIGPIPE.
+	 */
+	sigchain_push(SIGPIPE, SIG_IGN);
+
+	if (write_in_full(gpg.in, buffer->buf, buffer->len) != buffer->len) {
+		close(gpg.in);
+		close(gpg.out);
+		finish_command(&gpg);
+		return error(_("gpg did not accept the data"));
+	}
+	close(gpg.in);
+
+	bottom = signature->len;
+	len = strbuf_read(signature, gpg.out, 1024);
+	close(gpg.out);
+
+	sigchain_pop(SIGPIPE);
+
+	if (finish_command(&gpg) || !len || len < 0)
+		return error(_("gpg failed to sign the data"));
+
+	/* Strip CR from the line endings, in case we are on Windows. */
+	for (i = j = bottom; i < signature->len; i++)
+		if (signature->buf[i] != '\r') {
+			if (i != j)
+				signature->buf[j] = signature->buf[i];
+			j++;
+		}
+	strbuf_setlen(signature, j);
+
+	return 0;
+}
+
+/*
+ * Run "gpg" to see if the payload matches the detached signature.
+ * gpg_output_to tells where the output from "gpg" should go:
+ *   < 0: /dev/null
+ *   = 0: standard error of the calling process
+ *   > 0: the specified file descriptor
+ */
+int verify_signed_buffer(const char *payload, size_t payload_size,
+			 const char *signature, size_t signature_size,
+			 struct strbuf *gpg_output)
+{
+	struct child_process gpg;
+	const char *args_gpg[] = {"gpg", "--verify", "FILE", "-", NULL};
+	char path[PATH_MAX];
+	int fd, ret;
+
+	fd = git_mkstemp(path, PATH_MAX, ".git_vtag_tmpXXXXXX");
+	if (fd < 0)
+		return error("could not create temporary file '%s': %s",
+			     path, strerror(errno));
+	if (write_in_full(fd, signature, signature_size) < 0)
+		return error("failed writing detached signature to '%s': %s",
+			     path, strerror(errno));
+	close(fd);
+
+	memset(&gpg, 0, sizeof(gpg));
+	gpg.argv = args_gpg;
+	gpg.in = -1;
+	if (gpg_output)
+		gpg.err = -1;
+	args_gpg[2] = path;
+	if (start_command(&gpg)) {
+		unlink(path);
+		return error("could not run gpg.");
+	}
+
+	write_in_full(gpg.in, payload, payload_size);
+	close(gpg.in);
+
+	if (gpg_output)
+		strbuf_read(gpg_output, gpg.err, 0);
+	ret = finish_command(&gpg);
+
+	unlink_or_warn(path);
+
+	return ret;
+}
diff --git a/gpg-interface.h b/gpg-interface.h
@@ -0,0 +1,10 @@
+#ifndef GPG_INTERFACE_H
+#define GPG_INTERFACE_H
+
+extern int sign_buffer(struct strbuf *buffer, struct strbuf *signature, const char *signing_key);
+extern int verify_signed_buffer(const char *payload, size_t payload_size, const char *signature, size_t signature_size, struct strbuf *gpg_output);
+extern int git_gpg_config(const char *, const char *, void *);
+extern void set_signing_key(const char *);
+extern const char *get_signing_key(void);
+
+#endif
diff --git a/tag.c b/tag.c
@@ -139,6 +139,11 @@ int parse_tag(struct tag *item)
 	return ret;
 }
 
+/*
+ * Look at a signed tag object, and return the offset where
+ * the embedded detached signature begins, or the end of the
+ * data when there is no such signature.
+ */
 size_t parse_signature(const char *buf, unsigned long size)
 {
 	char *eol;

Original file line number	Diff line number	Diff line change
`@@ -139,6 +139,11 @@ int parse_tag(struct tag *item)`
`139`	`139`	`return ret;`
`140`	`140`	`}`
`141`	`141`
	`142`	`+/*`
	`143`	`+ * Look at a signed tag object, and return the offset where`
	`144`	`+ * the embedded detached signature begins, or the end of the`
	`145`	`+ * data when there is no such signature.`
	`146`	`+ */`
`142`	`147`	`size_t parse_signature(const char *buf, unsigned long size)`
`143`	`148`	`{`
`144`	`149`	`char *eol;`