src: add new error apis to prevent memory leaks

This PR creates two new externally-facing APIs, uv_err_name_r() and
uv_strerror_r().

In keeping with the precedent set by POSIX, the *_r() suffix of these
two new methods indicate that the caller does the memory management and
passes in the memory that the output will be stored in, which provides
an alternative for the two existent methods (uv_err_name() and
uv_strerror()), which, when called with an unknown error code, leak a
few bytes of memory.

PR-URL: https://github.com/libuv/libuv/pull/1898
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Santiago Gimeno santiago.gimeno@gmail.com

docs/src/errors.rst

@@ -335,11 +335,25 @@ API
     Returns the error message for the given error code.  Leaks a few bytes
     of memory when you call it with an unknown error code.
 
+.. c:function:: char* uv_strerror_r(int err, char* buf, size_t buflen)
+
+    Returns the error message for the given error code. The zero-terminated
+    message is stored in the user-supplied buffer `buf` of at most `buflen` bytes.
+
+    .. versionadded:: 1.22.0
+
 .. c:function:: const char* uv_err_name(int err)
 
     Returns the error name for the given error code.  Leaks a few bytes
     of memory when you call it with an unknown error code.
 
+.. c:function:: char* uv_err_name_r(int err, char* buf, size_t buflen)
+
+    Returns the error name for the given error code. The zero-terminated
+    name is stored in the user-supplied buffer `buf` of at most `buflen` bytes.
+
+    .. versionadded:: 1.22.0
+
 .. c:function:: int uv_translate_sys_error(int sys_errno)
 
    Returns the libuv error code equivalent to the given platform dependent error

include/uv.h

@@ -370,7 +370,10 @@ typedef enum {
 UV_EXTERN int uv_translate_sys_error(int sys_errno);
 
 UV_EXTERN const char* uv_strerror(int err);
+UV_EXTERN char* uv_strerror_r(int err, char* buf, size_t buflen);
+
 UV_EXTERN const char* uv_err_name(int err);
+UV_EXTERN char* uv_err_name_r(int err, char* buf, size_t buflen);
 
 
 #define UV_REQ_FIELDS                                                         \

src/uv-common.c

@@ -155,6 +155,18 @@ static const char* uv__unknown_err_code(int err) {
   return copy != NULL ? copy : "Unknown system error";
 }
 
+#define UV_ERR_NAME_GEN_R(name, _) \
+case UV_## name: \
+  snprintf(buf, buflen, "%s", #name); break;
+char* uv_err_name_r(int err, char* buf, size_t buflen) {
+  switch (err) {
+    UV_ERRNO_MAP(UV_ERR_NAME_GEN_R)
+    default: snprintf(buf, buflen, "Unknown system error %d", err);
+  }
+  return buf;
+}
+#undef UV_ERR_NAME_GEN_R
+
 
 #define UV_ERR_NAME_GEN(name, _) case UV_ ## name: return #name;
 const char* uv_err_name(int err) {
@@ -166,6 +178,19 @@ const char* uv_err_name(int err) {
 #undef UV_ERR_NAME_GEN
 
 
+#define UV_STRERROR_GEN_R(name, msg) \
+case UV_ ## name: \
+  snprintf(buf, buflen, "%s", msg); break;
+char* uv_strerror_r(int err, char* buf, size_t buflen) {
+  switch (err) {
+    UV_ERRNO_MAP(UV_STRERROR_GEN_R)
+    default: snprintf(buf, buflen, "Unknown system error %d", err);
+  }
+  return buf;
+}
+#undef UV_STRERROR_GEN_R
+
+
 #define UV_STRERROR_GEN(name, msg) case UV_ ## name: return msg;
 const char* uv_strerror(int err) {
   switch (err) {

test/test-error.c

@@ -37,6 +37,8 @@
  * See https://github.com/joyent/libuv/issues/210
  */
 TEST_IMPL(error_message) {
+  char buf[32];
+
   /* Cop out. Can't do proper checks on systems with
    * i18n-ized error messages...
    */
@@ -49,6 +51,10 @@ TEST_IMPL(error_message) {
   ASSERT(strcmp(uv_strerror(1337), "Unknown error") == 0);
   ASSERT(strcmp(uv_strerror(-1337), "Unknown error") == 0);
 
+  ASSERT(strstr(uv_strerror_r(UV_EINVAL, buf, sizeof(buf)), "Success") == NULL);
+  ASSERT(strstr(uv_strerror_r(1337, buf, sizeof(buf)), "1337") != NULL);
+  ASSERT(strstr(uv_strerror_r(-1337, buf, sizeof(buf)), "-1337") != NULL);
+
   return 0;
 }