From 81cb79620a361d7047c72be27d1ede48d5da4e93 Mon Sep 17 00:00:00 2001
From: m-holger <m.holger@qpdf.org>
Date: Wed, 4 Jun 2025 10:38:05 +0100
Subject: [PATCH] Refactor `is::OffsetBuffer` to remove dependency on `BufferInputSource`, improving encapsulation and maintainability.

---
 libqpdf/BufferInputSource.cc        | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 libqpdf/QPDFObjectHandle.cc         |  2 +-
 libqpdf/qpdf/InputSource_private.hh | 38 +++++++++++++++++++++-----------------
 3 files changed, 110 insertions(+), 18 deletions(-)

diff --git a/libqpdf/BufferInputSource.cc b/libqpdf/BufferInputSource.cc
index dae96f8..e124854 100644
--- a/libqpdf/BufferInputSource.cc
+++ b/libqpdf/BufferInputSource.cc
@@ -1,10 +1,15 @@
 #include <qpdf/BufferInputSource.hh>
+#include <qpdf/InputSource_private.hh>
 
+#include <qpdf/Buffer.hh>
 #include <qpdf/QIntC.hh>
+
 #include <algorithm>
 #include <cstring>
 #include <sstream>
 
+using namespace qpdf;
+
 BufferInputSource::BufferInputSource(std::string const& description, Buffer* buf, bool own_memory) :
     own_memory(own_memory),
     description(description),
@@ -139,3 +144,86 @@ BufferInputSource::unreadCh(char ch)
         --cur_offset;
     }
 }
+
+qpdf_offset_t
+is::OffsetBuffer::findAndSkipNextEOL_internal()
+{
+    if (cur_offset < 0) {
+        throw std::logic_error("INTERNAL ERROR: is::OffsetBuffer offset < 0");
+    }
+    qpdf_offset_t end_pos = max_offset;
+    if (cur_offset >= end_pos) {
+        last_offset = end_pos + global_offset;
+        cur_offset = end_pos;
+        return end_pos;
+    }
+
+    qpdf_offset_t result = 0;
+    unsigned char const* buffer = buf->getBuffer();
+    unsigned char const* end = buffer + end_pos;
+    unsigned char const* p = buffer + cur_offset;
+
+    while (p < end && !(*p == '\r' || *p == '\n')) {
+        ++p;
+    }
+    if (p < end) {
+        result = p - buffer;
+        cur_offset = result + 1;
+        ++p;
+        while (cur_offset < end_pos && (*p == '\r' || *p == '\n')) {
+            ++p;
+            ++cur_offset;
+        }
+    } else {
+        cur_offset = end_pos;
+        result = end_pos;
+    }
+    return result;
+}
+
+void
+is::OffsetBuffer::seek_internal(qpdf_offset_t offset, int whence)
+{
+    switch (whence) {
+    case SEEK_SET:
+        cur_offset = offset;
+        break;
+
+    case SEEK_END:
+        QIntC::range_check(max_offset, offset);
+        cur_offset = max_offset + offset;
+        break;
+
+    case SEEK_CUR:
+        QIntC::range_check(cur_offset, offset);
+        cur_offset += offset;
+        break;
+
+    default:
+        throw std::logic_error("INTERNAL ERROR: invalid argument to BufferInputSource::seek");
+        break;
+    }
+
+    if (cur_offset < 0) {
+        throw std::runtime_error(description + ": seek before beginning of buffer");
+    }
+}
+
+size_t
+is::OffsetBuffer::read(char* buffer, size_t length)
+{
+    if (cur_offset < 0) {
+        throw std::logic_error("INTERNAL ERROR: is::OffsetBuffer offset < 0");
+    }
+    qpdf_offset_t end_pos = max_offset;
+    if (cur_offset >= end_pos) {
+        last_offset = end_pos + global_offset;
+        return 0;
+    }
+
+    last_offset = cur_offset + global_offset;
+    size_t len = std::min(QIntC::to_size(end_pos - cur_offset), length);
+    memcpy(buffer, buf->getBuffer() + cur_offset, len);
+    cur_offset += QIntC::to_offset(len);
+    return len;
+}
diff --git a/libqpdf/QPDFObjectHandle.cc b/libqpdf/QPDFObjectHandle.cc
index 440e3e5..84d88d3 100644
--- a/libqpdf/QPDFObjectHandle.cc
+++ b/libqpdf/QPDFObjectHandle.cc
@@ -2,7 +2,7 @@
 
 #include <qpdf/QPDFObjectHandle_private.hh>
 
-#include <qpdf/InputSource_private.hh>
+#include <qpdf/BufferInputSource.hh>
 #include <qpdf/JSON_writer.hh>
 #include <qpdf/Pipeline_private.hh>
 #include <qpdf/Pl_Buffer.hh>
diff --git a/libqpdf/qpdf/InputSource_private.hh b/libqpdf/qpdf/InputSource_private.hh
index 00d27c9..84ecc75 100644
--- a/libqpdf/qpdf/InputSource_private.hh
+++ b/libqpdf/qpdf/InputSource_private.hh
@@ -1,7 +1,7 @@
 #ifndef QPDF_INPUTSOURCE_PRIVATE_HH
 #define QPDF_INPUTSOURCE_PRIVATE_HH
 
-#include <qpdf/BufferInputSource.hh>
+#include <qpdf/Buffer.hh>
 #include <qpdf/InputSource.hh>
 
 #include <limits>
@@ -14,7 +14,9 @@ namespace qpdf::is
     {
       public:
         OffsetBuffer(std::string const& description, Buffer* buf, qpdf_offset_t global_offset) :
-            proxied(description, buf),
+            description(description),
+            buf(buf),
+            max_offset(buf ? static_cast<qpdf_offset_t>(buf->getSize()) : 0),
             global_offset(global_offset)
         {
             if (global_offset < 0) {
@@ -28,53 +30,55 @@ namespace qpdf::is
         qpdf_offset_t
         findAndSkipNextEOL() final
         {
-            return proxied.findAndSkipNextEOL() + global_offset;
+            return findAndSkipNextEOL_internal() + global_offset;
         }
 
         std::string const&
         getName() const final
         {
-            return proxied.getName();
+            return description;
         }
 
         qpdf_offset_t
         tell() final
         {
-            return proxied.tell() + global_offset;
+            return cur_offset + global_offset;
         }
 
         void
         seek(qpdf_offset_t offset, int whence) final
         {
             if (whence == SEEK_SET) {
-                proxied.seek(offset - global_offset, whence);
+                seek_internal(offset - global_offset, whence);
             } else {
-                proxied.seek(offset, whence);
+                seek_internal(offset, whence);
             }
         }
 
         void
         rewind() final
         {
-            seek(0, SEEK_SET);
+            seek_internal(0, SEEK_SET);
         }
 
-        size_t
-        read(char* buffer, size_t length) final
-        {
-            size_t result = proxied.read(buffer, length);
-            setLastOffset(proxied.getLastOffset() + global_offset);
-            return result;
-        }
+        size_t read(char* buffer, size_t length) final;
 
         void
         unreadCh(char ch) final
         {
-            proxied.unreadCh(ch);
+            if (cur_offset > 0) {
+                --cur_offset;
+            }
         }
 
       private:
-        BufferInputSource proxied;
+        qpdf_offset_t findAndSkipNextEOL_internal();
+        void seek_internal(qpdf_offset_t offset, int whence);
+
+        std::string description;
+        Buffer* buf;
+        qpdf_offset_t cur_offset{0};
+        qpdf_offset_t max_offset;
         qpdf_offset_t global_offset;
     };
 
--
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