From f60bea0fdd7067d1645a805e05cc4a6f4ceffa7a Mon Sep 17 00:00:00 2001
From: Evan Burkey <evan@burkey.co>
Date: Thu, 28 Mar 2024 19:09:39 -0700
Subject: [PATCH] add hex_encode

---
 docs/crypto.md     | 20 ++++++++++++++++++--
 include/lfcrypto.h |  3 ++-
 src/crypto.c       | 18 ++++++++++++++++--
 tests/tests.c      |  4 ++++
 4 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/docs/crypto.md b/docs/crypto.md
index 7b6c419..33714eb 100644
--- a/docs/crypto.md
+++ b/docs/crypto.md
@@ -23,16 +23,32 @@ in case you need to know the size of the decoded data, otherwise you can just pa
 unsigned char *b64_decode(const char *s, size_t sz, size_t *decode_sz);
 ```
 
+### hex_encode
+
+Encodes an array of bytes into a string in hex representation. For example, converts 
+`[0xDE, 0xAD, 0xBE, 0xEF]` into `"DEADBEEF"`. The returned string will always be in capital
+letters with no leading `0x`. User is responsible for the freeing of the returned string
+
+```c
+const char *hex_encode(const unsigned char *hex, size_t sz);
+
+// Example
+const char *s = hex_encode(h, 4);
+assert(strcmp(s, "DEADBEEF") == 0);
+free(s);
+```
+
 ### hex_decode
 
 Decodes a string of characters representing hexadecimal bytes into an array of `unsigned char`.
-For example, converts `"DEADBEEF"` into `[0xDE, 0xAD, 0xBE, 0xEF]`.
+For example, converts `"DEADBEEF"` into `[0xDE, 0xAD, 0xBE, 0xEF]`. User is reponsible for the
+freeing of the returned byte array
 
 ```c
 unsigned char *hex_decode(const char *orig, size_t *sz);
 
 // Example
-s = hex_decode("DEADBEEF", &s_sz);
+unsigned char *s = hex_decode("DEADBEEF", &s_sz);
 unsigned char h[4] = {
     0xDE, 0xAD, 0xBE, 0xEF
 };
diff --git a/include/lfcrypto.h b/include/lfcrypto.h
index 7a07405..0771811 100644
--- a/include/lfcrypto.h
+++ b/include/lfcrypto.h
@@ -3,8 +3,9 @@
 
 #include <stddef.h>
 
-unsigned char *b64_encode(const unsigned char *s, size_t sz);
+const char *b64_encode(const unsigned char *s, size_t sz);
 unsigned char *b64_decode(const char *s, size_t sz, size_t *decode_sz);
+const char *hex_encode(const unsigned char *hex, size_t sz);
 unsigned char *hex_decode(const char *orig, size_t *sz);
 
 #endif // LIBFLINT_CRYPTO_H
diff --git a/src/crypto.c b/src/crypto.c
index 4795e3d..0286f8c 100644
--- a/src/crypto.c
+++ b/src/crypto.c
@@ -45,7 +45,7 @@ static int resize_b64_buf(b64_buf *b, size_t sz) {
     return 0;
 }
 
-unsigned char *b64_encode(const unsigned char *s, size_t sz) {
+const char *b64_encode(const unsigned char *s, size_t sz) {
     int i = 0;
     b64_buf encbuf;
     size_t size = 0;
@@ -110,7 +110,7 @@ unsigned char *b64_encode(const unsigned char *s, size_t sz) {
     }
     encbuf.ptr[size] = '\0';
 
-    return encbuf.ptr;
+    return (char *)encbuf.ptr;
 }
 
 unsigned char *b64_decode(const char *s, size_t sz, size_t *decode_sz) {
@@ -229,3 +229,17 @@ unsigned char *hex_decode(const char *orig, size_t *sz) {
     free(buf);
     return hex;
 }
+
+const char *hex_encode(const unsigned char *hex, size_t sz) {
+    size_t ssz = sz * 2 + 1;
+    char *s = malloc(sizeof(char) * ssz);
+    char *pos = s;
+
+    for (size_t i = 0; i < sz; ++i) {
+        snprintf(pos, 3, "%2X", hex[i]);
+        pos += 2;
+    }
+    s[ssz - 1] = '\0';
+
+    return s;
+}
diff --git a/tests/tests.c b/tests/tests.c
index 142b87a..5193efa 100644
--- a/tests/tests.c
+++ b/tests/tests.c
@@ -345,6 +345,10 @@ void test_crypto() {
         assert(s[i] == h2[i]);
     }
     free(s);
+
+    s = hex_encode(h, 4);
+    assert(strcmp(s, "DEADBEEF") == 0);
+    free(s);
 }
 
 #if defined(__APPLE__) || defined(__MACH__)