From a81fd6242d4a4076b7c79213de8cc7e13a311e56 Mon Sep 17 00:00:00 2001
From: Michael Vrable <mvrable@cs.ucsd.edu>
Date: Sat, 23 Dec 2006 17:19:58 -0800
Subject: [PATCH] Improve comments, and track number of bytes written to a
 stream.

---
 store.cc | 15 +++++++++++++--
 store.h  | 52 ++++++++++++++++++++++++++++++++++++++++++----------
 2 files changed, 55 insertions(+), 12 deletions(-)

diff --git a/store.cc b/store.cc
index 5df4b77..6770e1c 100644
--- a/store.cc
+++ b/store.cc
@@ -11,6 +11,17 @@
 
 using std::string;
 
+OutputStream::OutputStream()
+    : bytes_written(0)
+{
+}
+
+void OutputStream::write(const void *data, size_t len)
+{
+    write_internal(data, len);
+    bytes_written += len;
+}
+
 void OutputStream::write_u8(uint8_t val)
 {
     write(&val, 1);
@@ -95,7 +106,7 @@ StringOutputStream::StringOutputStream()
 {
 }
 
-void StringOutputStream::write(const void *data, size_t len)
+void StringOutputStream::write_internal(const void *data, size_t len)
 {
     buf.write((const char *)data, len);
     if (!buf.good())
@@ -112,7 +123,7 @@ FileOutputStream::~FileOutputStream()
     fclose(f);
 }
 
-void FileOutputStream::write(const void *data, size_t len)
+void FileOutputStream::write_internal(const void *data, size_t len)
 {
     size_t res;
 
diff --git a/store.h b/store.h
index 7950297..3725a9f 100644
--- a/store.h
+++ b/store.h
@@ -15,8 +15,14 @@
 #include <string>
 #include <sstream>
 
+/* In memory datatype to represent key/value pairs of information, such as file
+ * metadata.  Currently implemented as map<string, string>. */
 typedef std::map<std::string, std::string> dictionary;
 
+/* IOException will be thrown if an error occurs while reading or writing in
+ * one of the I/O wrappers.  Depending upon the context; this may be fatal or
+ * not--typically, errors reading/writing the store will be serious, but errors
+ * reading an individual file are less so. */
 class IOException : public std::exception {
 private:
     std::string error;
@@ -26,13 +32,22 @@ public:
     std::string getError() const { return error; }
 };
 
+/* OutputStream is an abstract interface for writing data without seeking.
+ * Output could be to a file, to an object within a segment, or even to a
+ * memory buffer to help serialize data. */
 class OutputStream {
 public:
+    OutputStream();
     virtual ~OutputStream() { }
-    virtual void write(const void *data, size_t len) = 0;
 
-    /* Convenience functions for writing other data types.  Values are always
-     * written out in little-endian order. */
+    // Write the given data buffer
+    void write(const void *data, size_t len);
+
+    // Return the total number of bytes written so far
+    int64_t get_pos() const { return bytes_written; }
+
+    // Convenience functions for writing other data types.  Values are always
+    // written out in little-endian order.
     void write_u8(uint8_t val);
     void write_u16(uint16_t val);
     void write_u32(uint32_t val);
@@ -45,28 +60,45 @@ public:
 
     void write_string(const std::string &s);
     void write_dictionary(const dictionary &d);
+
+protected:
+    // Function which actually causes a write: must be overridden by
+    // implementation.
+    virtual void write_internal(const void *data, size_t len) = 0;
+
+private:
+    int64_t bytes_written;
 };
 
+/* An OutputStream implementation which writes data to memory and returns the
+ * result as a string. */
 class StringOutputStream : public OutputStream {
-private:
-    std::stringstream buf;
 public:
     StringOutputStream();
-
-    virtual void write(const void *data, size_t len);
     std::string contents() const { return buf.str(); }
+
+protected:
+    virtual void write_internal(const void *data, size_t len);
+
+private:
+    std::stringstream buf;
 };
 
+/* An OutputStream implementation which writes data via the C stdio layer. */
 class FileOutputStream : public OutputStream {
-private:
-    FILE *f;
 public:
     explicit FileOutputStream(FILE *file);
     virtual ~FileOutputStream();
 
-    virtual void write(const void *data, size_t len);
+protected:
+    virtual void write_internal(const void *data, size_t len);
+
+private:
+    FILE *f;
 };
 
+/* Simple wrappers that encode integers using a StringOutputStream and return
+ * the encoded result. */
 std::string encode_u16(uint16_t val);
 std::string encode_u32(uint32_t val);
 std::string encode_u64(uint64_t val);
-- 
2.20.1