Add abbreviated_string() to sha* classes

3 files changed, 29 insertions, 9 deletions

diff --git a/libbutl/sha1.mxx b/libbutl/sha1.mxx
index 5259189..7ba3c0a 100644
--- a/libbutl/sha1.mxx
+++ b/libbutl/sha1.mxx
@@ -77,6 +77,12 @@ LIBBUTL_MODEXPORT namespace butl
     const char*
     string () const;
 
+    std::string
+    abbreviated_string (std::size_t n) const
+    {
+      return std::string (string (), n < 40 ? n : 40);
+    }
+
   private:
     struct context // Note: identical to SHA1_CTX.
     {
diff --git a/libbutl/sha256.cxx b/libbutl/sha256.cxx
index be29871..694b331 100644
--- a/libbutl/sha256.cxx
+++ b/libbutl/sha256.cxx
@@ -122,7 +122,7 @@ namespace butl
 
     string f;
     f.reserve (n + 31);
-    for (size_t i (0); i < n; ++i)
+    for (size_t i (0); i != n; ++i)
     {
       char c (s[i]);
       if (!isxdigit (c))
@@ -138,7 +138,7 @@ namespace butl
   }
 
   string
-  fingerprint_to_sha256 (const string& f)
+  fingerprint_to_sha256 (const string& f, size_t rn)
   {
     auto bad = []() {throw invalid_argument ("invalid fingerprint");};
 
@@ -146,9 +146,16 @@ namespace butl
     if (n != 32 * 3 - 1)
       bad ();
 
+    if (rn > 64)
+      rn = 64;
+
     string s;
-    s.reserve (64);
-    for (size_t i (0); i < n; ++i)
+    s.reserve (rn);
+
+    // Note that we continue to validate the fingerprint after the result is
+    // ready.
+    //
+    for (size_t i (0); i != n; ++i)
     {
       char c (f[i]);
       if ((i + 1) % 3 == 0)
@@ -161,7 +168,8 @@ namespace butl
         if (!isxdigit (c))
           bad ();
 
-        s += lcase (c);
+        if (s.size () != rn)
+          s += lcase (c);
       }
     }
 
diff --git a/libbutl/sha256.mxx b/libbutl/sha256.mxx
index 23a116a..1584be8 100644
--- a/libbutl/sha256.mxx
+++ b/libbutl/sha256.mxx
@@ -111,6 +111,12 @@ LIBBUTL_MODEXPORT namespace butl
     const char*
     string () const;
 
+    std::string
+    abbreviated_string (std::size_t n) const
+    {
+      return std::string (string (), n < 64 ? n : 64);
+    }
+
   private:
     struct context // Note: identical to SHA256_CTX.
     {
@@ -137,10 +143,10 @@ LIBBUTL_MODEXPORT namespace butl
   LIBBUTL_SYMEXPORT std::string
   sha256_to_fingerprint (const std::string&);
 
-  // Convert a fingerprint (32 colon-separated hex digit pairs) to the SHA256
-  // string representation (64 lower case hex digits). Throw invalid_argument
-  // if the argument is not a valid fingerprint.
+  // Convert a fingerprint (32 colon-separated hex digit pairs) to the possibly
+  // abbreviated SHA256 string representation (up to 64 lower case hex digits).
+  // Throw invalid_argument if the first argument is not a valid fingerprint.
   //
   LIBBUTL_SYMEXPORT std::string
-  fingerprint_to_sha256 (const std::string&);
+  fingerprint_to_sha256 (const std::string&, std::size_t = 64);
 }