Write a test for OBJ_obj2txt.

OBJ_obj2txt's implementation is kind of scary. Also it casts between int
and size_t a lot. In preparation for rewriting it, add a test.

Change-Id: Iefb1d0cddff58d67e5b04ec332477aab8aa687b6
Reviewed-on: https://boringssl-review.googlesource.com/9130
Reviewed-by: Adam Langley <agl@google.com>

crypto/obj/obj_test.cc

@@ -15,6 +15,7 @@
 #include <stdio.h>
 #include <string.h>
 
+#include <openssl/asn1.h>
 #include <openssl/bytestring.h>
 #include <openssl/crypto.h>
 #include <openssl/obj.h>
@@ -93,11 +94,103 @@ static bool TestSignatureAlgorithms() {
   return true;
 }
 
+static bool ExpectObj2Txt(const uint8_t *der, size_t der_len,
+                          bool dont_return_name,
+                          const char *expected) {
+  ASN1_OBJECT obj;
+  memset(&obj, 0, sizeof(obj));
+  obj.data = der;
+  obj.length = static_cast<int>(der_len);
+
+  int expected_len = static_cast<int>(strlen(expected));
+
+  int len = OBJ_obj2txt(nullptr, 0, &obj, dont_return_name);
+  if (len != expected_len) {
+    fprintf(stderr,
+            "OBJ_obj2txt of %s with out_len = 0 returned %d, wanted %d.\n",
+            expected, len, expected_len);
+    return false;
+  }
+
+  char short_buf[1];
+  memset(short_buf, 0xff, sizeof(short_buf));
+  len = OBJ_obj2txt(short_buf, sizeof(short_buf), &obj, dont_return_name);
+  if (len != expected_len) {
+    fprintf(stderr,
+            "OBJ_obj2txt of %s with out_len = 1 returned %d, wanted %d.\n",
+            expected, len, expected_len);
+    return false;
+  }
+
+  if (memchr(short_buf, '\0', sizeof(short_buf)) == nullptr) {
+    fprintf(stderr,
+            "OBJ_obj2txt of %s with out_len = 1 did not NUL-terminate the "
+            "output.\n",
+            expected);
+    return false;
+  }
+
+  char buf[256];
+  len = OBJ_obj2txt(buf, sizeof(buf), &obj, dont_return_name);
+  if (len != expected_len) {
+    fprintf(stderr,
+            "OBJ_obj2txt of %s with out_len = 256 returned %d, wanted %d.\n",
+            expected, len, expected_len);
+    return false;
+  }
+
+  if (strcmp(buf, expected) != 0) {
+    fprintf(stderr, "OBJ_obj2txt returned \"%s\"; wanted \"%s\".\n", buf,
+            expected);
+    return false;
+  }
+
+  return true;
+}
+
+static bool TestObj2Txt() {
+  // kSHA256WithRSAEncryption is the DER representation of
+  // 1.2.840.113549.1.1.11, id-sha256WithRSAEncryption.
+  static const uint8_t kSHA256WithRSAEncryption[] = {
+      0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x0b,
+  };
+
+  // kBasicConstraints is the DER representation of 2.5.29.19,
+  // id-basicConstraints.
+  static const uint8_t kBasicConstraints[] = {
+      0x55, 0x1d, 0x13,
+  };
+
+  // kTestOID is the DER representation of 1.2.840.113554.4.1.72585.0,
+  // from https://davidben.net/oid.
+  static const uint8_t kTestOID[] = {
+      0x2a, 0x86, 0x48, 0x86, 0xf7, 0x12, 0x04, 0x01, 0x84, 0xb7, 0x09, 0x00,
+  };
+
+  if (!ExpectObj2Txt(kSHA256WithRSAEncryption, sizeof(kSHA256WithRSAEncryption),
+                     true /* don't return name */, "1.2.840.113549.1.1.11") ||
+      !ExpectObj2Txt(kSHA256WithRSAEncryption, sizeof(kSHA256WithRSAEncryption),
+                     false /* return name */, "sha256WithRSAEncryption") ||
+      !ExpectObj2Txt(kBasicConstraints, sizeof(kBasicConstraints),
+                     true /* don't return name */, "2.5.29.19") ||
+      !ExpectObj2Txt(kBasicConstraints, sizeof(kBasicConstraints),
+                     false /* return name */, "X509v3 Basic Constraints") ||
+      !ExpectObj2Txt(kTestOID, sizeof(kTestOID), true /* don't return name */,
+                     "1.2.840.113554.4.1.72585.0") ||
+      !ExpectObj2Txt(kTestOID, sizeof(kTestOID), false /* return name */,
+                     "1.2.840.113554.4.1.72585.0")) {
+    return false;
+  }
+
+  return true;
+}
+
 int main() {
   CRYPTO_library_init();
 
   if (!TestBasic() ||
-      !TestSignatureAlgorithms()) {
+      !TestSignatureAlgorithms() ||
+      !TestObj2Txt()) {
     return 1;
   }