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Drain tar stderr while streaming archives #800

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Drain tar stderr while streaming archives #800

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59 changes: 49 additions & 10 deletions src/as-utils.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2493,6 +2493,27 @@ as_utils_tar_child_setup (gpointer user_data)
}
#endif

/**
* as_utils_tar_stderr_drain_cb:
*
* Drain tar's stderr to EOF, retaining up to 4096 bytes for diagnostics.
*/
static gpointer
as_utils_tar_stderr_drain_cb (gpointer data)
{
GString *diagnostic = g_string_new ("");
gssize bytes_read;
gchar buffer[4096];

while ((bytes_read = g_input_stream_read (data, buffer, sizeof (buffer), NULL, NULL)) > 0) {
/* Keep draining even after the diagnostic buffer is full. */
g_string_append_len (diagnostic,
buffer,
MIN ((gsize) bytes_read, sizeof (buffer) - diagnostic->len));
}
return diagnostic;
}

/**
* as_utils_extract_tarball:
*
Expand All @@ -2508,6 +2529,9 @@ as_utils_extract_tarball (const gchar *filename, const gchar *target_dir, GError
g_autoptr(GSubprocessLauncher) launcher = NULL;
g_autoptr(GSubprocess) tar_process = NULL;
GOutputStream *tar_stdin = NULL;
g_autoptr(GString) stderr_buf = NULL;
GThread *stderr_thread;
gboolean ret = FALSE;
gssize bytes_read;
gchar buffer[4096];
GError *tmp_error = NULL;
Expand Down Expand Up @@ -2559,6 +2583,12 @@ as_utils_extract_tarball (const gchar *filename, const gchar *target_dir, GError
return FALSE;
}

/* Drain stderr concurrently so tar cannot block on a full pipe while
* we write the archive to its stdin. */
stderr_thread = g_thread_new ("as-tar-stderr-drain",
as_utils_tar_stderr_drain_cb,
g_subprocess_get_stderr_pipe (tar_process));

tar_stdin = g_subprocess_get_stdin_pipe (tar_process);

/* read decompressed data from the tarball and write it to the tar subprocess */
Expand All @@ -2569,32 +2599,33 @@ as_utils_extract_tarball (const gchar *filename, const gchar *target_dir, GError
&tmp_error)) > 0) {
if (!g_output_stream_write_all (tar_stdin, buffer, bytes_read, NULL, NULL, error)) {
g_prefix_error (error, "Error writing to tar subprocess: ");
return FALSE;
goto out;
}
}

/* close the input stream to tar */
if (!g_output_stream_close (tar_stdin, NULL, error)) {
g_prefix_error (error, "Error closing tar subprocess stdin: ");
return FALSE;
goto out;
}

if (tmp_error != NULL) {
g_propagate_prefixed_error (error, tmp_error, "Error reading tarball: ");
return FALSE;
goto out;
}

/* wait for the subprocess to finish and check for errors */
if (!g_subprocess_wait_check (tar_process, NULL, &tmp_error)) {
g_autoptr(GBytes) stderr_bytes = NULL;
g_autoptr(GString) error_msg = NULL;
const gchar *stderr_data;
gsize stderr_size;
GInputStream *tar_stderr = NULL;

tar_stderr = g_subprocess_get_stderr_pipe (tar_process);
stderr_bytes = g_input_stream_read_bytes (tar_stderr, 4096, NULL, NULL);
stderr_data = g_bytes_get_data (stderr_bytes, &stderr_size);
/* Process exit does not mean all buffered stderr has been consumed. */
stderr_buf = g_thread_join (stderr_thread);
stderr_thread = NULL;

stderr_data = stderr_buf->str;
stderr_size = stderr_buf->len;

error_msg = g_string_new ("Tarball extraction failed");
if (stderr_size > 0) {
Expand Down Expand Up @@ -2623,10 +2654,18 @@ as_utils_extract_tarball (const gchar *filename, const gchar *target_dir, GError
g_subprocess_get_exit_status (tar_process));
}

return FALSE;
goto out;
}

return TRUE;
ret = TRUE;
out:
/* Closing stdin lets tar exit before we join the drain thread. */
if (stderr_thread != NULL) {
if (!g_output_stream_is_closed (tar_stdin))
g_output_stream_close (tar_stdin, NULL, NULL);
stderr_buf = g_thread_join (stderr_thread);
}
return ret;
}

/**
Expand Down
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