Added a function "computeBytesBeforeWidth"

src/Common/UTF8Helpers.cpp

@@ -89,7 +89,18 @@ static int wcwidth(wchar_t wc)
     }
 }
 
-size_t computeWidth(const UInt8 * data, size_t size, size_t prefix) noexcept
+
+namespace
+{
+
+enum ComputeWidthMode
+{
+    Width,              /// Calcualte and return visible width
+    BytesBeforLimit     /// Calculate and return the maximum number of bytes when substring fits in visible width.
+};
+
+template <ComputeWidthMode mode>
+static size_t computeWidthImpl(const UInt8 * data, size_t size, size_t prefix, size_t limit) noexcept
 {
     UTF8Decoder decoder;
     size_t width = 0;
@@ -132,16 +143,22 @@ size_t computeWidth(const UInt8 * data, size_t size, size_t prefix) noexcept
             ++i;
         }
 
+        if (mode == BytesBeforLimit && width >= limit)
+            return i - (width - limit);
+
         switch (decoder.decode(data[i]))
         {
             case UTF8Decoder::REJECT:
+            {
                 decoder.reset();
                 // invalid sequences seem to have zero width in modern terminals
                 // tested in libvte-based, alacritty, urxvt and xterm
                 i -= rollback;
                 rollback = 0;
                 break;
+            }
             case UTF8Decoder::ACCEPT:
+            {
                 // there are special control characters that manipulate the terminal output.
                 // (`0x08`, `0x09`, `0x0a`, `0x0b`, `0x0c`, `0x0d`, `0x1b`)
                 // Since we don't touch the original column data, there is no easy way to escape them.
@@ -149,12 +166,19 @@ size_t computeWidth(const UInt8 * data, size_t size, size_t prefix) noexcept
                 // TODO: multiline support for '\n'
 
                 // special treatment for '\t'
+                size_t next_width = width;
                 if (decoder.codepoint == '\t')
-                    width += 8 - (prefix + width) % 8;
+                    next_width += 8 - (prefix + width) % 8;
                 else
-                    width += wcwidth(decoder.codepoint);
+                    next_width += wcwidth(decoder.codepoint);
+
+                if (mode == BytesBeforLimit && next_width >= limit)
+                    return i - rollback;
+                width = next_width;
+
                 rollback = 0;
                 break;
+            }
             // continue if we meet other values here
             default:
                 ++rollback;
@@ -162,7 +186,21 @@ size_t computeWidth(const UInt8 * data, size_t size, size_t prefix) noexcept
     }
 
     // no need to handle trailing sequence as they have zero width
-    return width;
-}
+    return (mode == BytesBeforLimit) ? size : width;
+}
+
+}
+
+
+size_t computeWidth(const UInt8 * data, size_t size, size_t prefix) noexcept
+{
+    return computeWidthImpl<Width>(data, size, prefix, 0);
+}
+
+size_t computeBytesBeforeWidth(const UInt8 * data, size_t size, size_t prefix, size_t limit) noexcept
+{
+    return computeWidthImpl<BytesBeforLimit>(data, size, prefix, limit);
+}
+
 }
 }