tls_openssl: Improve quality of printed error messages, pass IO error codes through

Print every error in the stack, if more than one, and don't print
bogus errors if there's none logged within OpenSSL.

Retain the underlying IO error code, print an error message out of
it, and pass the error code on to the caller.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/tls_openssl.c

@@ -46,6 +46,7 @@ typedef struct TLSContext {
 #if OPENSSL_VERSION_NUMBER >= 0x1010000fL
     BIO_METHOD* url_bio_method;
 #endif
+    int io_err;
 } TLSContext;
 
 #if HAVE_THREADS && OPENSSL_VERSION_NUMBER < 0x10100000L
@@ -124,13 +125,25 @@ void ff_openssl_deinit(void)
 static int print_tls_error(URLContext *h, int ret)
 {
     TLSContext *c = h->priv_data;
+    int printed = 0, e, averr = AVERROR(EIO);
     if (h->flags & AVIO_FLAG_NONBLOCK) {
         int err = SSL_get_error(c->ssl, ret);
         if (err == SSL_ERROR_WANT_READ || err == SSL_ERROR_WANT_WRITE)
             return AVERROR(EAGAIN);
     }
-    av_log(h, AV_LOG_ERROR, "%s\n", ERR_error_string(ERR_get_error(), NULL));
-    return AVERROR(EIO);
+    while ((e = ERR_get_error()) != 0) {
+        av_log(h, AV_LOG_ERROR, "%s\n", ERR_error_string(e, NULL));
+        printed = 1;
+    }
+    if (c->io_err) {
+        av_log(h, AV_LOG_ERROR, "IO error: %s\n", av_err2str(c->io_err));
+        printed = 1;
+        averr = c->io_err;
+        c->io_err = 0;
+    }
+    if (!printed)
+        av_log(h, AV_LOG_ERROR, "Unknown error\n");
+    return averr;
 }
 
 static int tls_close(URLContext *h)
@@ -178,29 +191,33 @@ static int url_bio_destroy(BIO *b)
 
 static int url_bio_bread(BIO *b, char *buf, int len)
 {
-    URLContext *h = GET_BIO_DATA(b);
-    int ret = ffurl_read(h, buf, len);
+    TLSContext *c = GET_BIO_DATA(b);
+    int ret = ffurl_read(c->tls_shared.tcp, buf, len);
     if (ret >= 0)
         return ret;
     BIO_clear_retry_flags(b);
-    if (ret == AVERROR(EAGAIN))
-        BIO_set_retry_read(b);
     if (ret == AVERROR_EXIT)
         return 0;
+    if (ret == AVERROR(EAGAIN))
+        BIO_set_retry_read(b);
+    else
+        c->io_err = ret;
     return -1;
 }
 
 static int url_bio_bwrite(BIO *b, const char *buf, int len)
 {
-    URLContext *h = GET_BIO_DATA(b);
-    int ret = ffurl_write(h, buf, len);
+    TLSContext *c = GET_BIO_DATA(b);
+    int ret = ffurl_write(c->tls_shared.tcp, buf, len);
     if (ret >= 0)
         return ret;
     BIO_clear_retry_flags(b);
-    if (ret == AVERROR(EAGAIN))
-        BIO_set_retry_write(b);
     if (ret == AVERROR_EXIT)
         return 0;
+    if (ret == AVERROR(EAGAIN))
+        BIO_set_retry_write(b);
+    else
+        c->io_err = ret;
     return -1;
 }
 
@@ -291,10 +308,10 @@ static int tls_open(URLContext *h, const char *uri, int flags, AVDictionary **op
     BIO_meth_set_create(p->url_bio_method, url_bio_create);
     BIO_meth_set_destroy(p->url_bio_method, url_bio_destroy);
     bio = BIO_new(p->url_bio_method);
-    BIO_set_data(bio, c->tcp);
+    BIO_set_data(bio, p);
 #else
     bio = BIO_new(&url_bio_method);
-    bio->ptr = c->tcp;
+    bio->ptr = p;
 #endif
     SSL_set_bio(p->ssl, bio, bio);
     if (!c->listen && !c->numerichost)