xref: /system/ulib/fbl/include/fbl/string_buffer.h

// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#pragma once

#include "string.h"
#include <stdarg.h>

#include <fbl/string.h>
#include <fbl/string_piece.h>
#include <zircon/assert.h>
#include <zircon/compiler.h>

namespace fbl {
namespace internal {
size_t StringBufferAppendPrintf(char* dest, size_t remaining,
                                const char* format, va_list ap);
} // namespace internal

// A fixed-size buffer for assembling a string.
//
// fbl::StringBuffer is designed to resemble std::string except that it
// does not allocate heap storage.
//
// The buffer is sized to hold up to N characters plus a null-terminator.
template <size_t N>
class StringBuffer final {
public:
    // Creates an empty string buffer.
    StringBuffer()
        : length_(0u) {
        data_[0] = 0;
    }

    // Releases the string buffer.
    ~StringBuffer() = default;

    // Returns a pointer to the null-terminated contents of the string.
    char* data() { return data_; }
    const char* data() const { return data_; }
    const char* c_str() const { return data_; }

    // Returns the length of the string, excluding its null terminator.
    size_t length() const { return length_; }
    size_t size() const { return length_; }

    // Returns the length of the string, excluding its null terminator.
    bool empty() const { return length_ == 0u; }

    // Returns the capacity of the buffer.
    constexpr size_t capacity() const { return N; }

    // Character iterators, excluding the null terminator.
    char* begin() { return data(); }
    const char* begin() const { return data(); }
    const char* cbegin() const { return data(); }
    char* end() { return data() + length(); }
    const char* end() const { return data() + length(); }
    const char* cend() const { return data() + length(); }

    // Gets a reference to the character at the specified index.
    // Position must be greater than or equal to 0 and less than |length()|.
    char& operator[](size_t pos) { return data_[pos]; }
    const char& operator[](size_t pos) const { return data_[pos]; }

    // Clears the string buffer.
    void Clear() {
        length_ = 0u;
        data_[0] = 0;
    }

    // Resizes the string buffer.
    // If the current length is less than |count|, additional characters are appended
    // with the value |ch|.
    // If the current length is greater than |count|, the string is truncated.
    // |length| must be less than or equal to |N|.
    void Resize(size_t count, char ch = '\0') {
        ZX_DEBUG_ASSERT(count <= N);
        if (length_ < count)
            memset(data_ + length_, ch, count - length_);
        length_ = count;
        data_[length_] = 0;
    }

    // Appends a single character.
    // The result is truncated if the appended content does not fit completely.
    StringBuffer& Append(char ch) {
        if (length_ < N) {
            data_[length_++] = ch;
            data_[length_] = 0;
        }
        return *this;
    }

    // Appends content to the string buffer from a null-terminated C string.
    // The result is truncated if the appended content does not fit completely.
    // |data| must not be null.
    StringBuffer& Append(const char* data) {
        Append(data, constexpr_strlen(data));
        return *this;
    }

    // Appends content to the string buffer from a character array of given length.
    // The result is truncated if the appended content does not fit completely.
    // |data| must not be null.
    StringBuffer& Append(const char* data, size_t length) {
        AppendInternal(data, length);
        return *this;
    }

    // Appends content to the string buffer from a string piece.
    // The result is truncated if the appended content does not fit completely.
    StringBuffer& Append(const fbl::StringPiece& piece) {
        AppendInternal(piece.data(), piece.length());
        return *this;
    }

    // Appends content to the string buffer from another string.
    // The result is truncated if the appended content does not fit completely.
    StringBuffer& Append(const fbl::String& other) {
        AppendInternal(other.data(), other.length());
        return *this;
    }

    // Appends |printf()|-like input.
    // The result is truncated if the appended content does not fit completely.
    StringBuffer& AppendPrintf(const char* format, ...) __PRINTFLIKE(2, 3) {
        va_list ap;
        va_start(ap, format);
        AppendVPrintf(format, ap);
        va_end(ap);
        return *this;
    }

    // Appends |vprintf()|-like input using a |va_list|.
    // The result is truncated if the appended content does not fit completely.
    StringBuffer& AppendVPrintf(const char* format, va_list ap) {
        length_ += internal::StringBufferAppendPrintf(
            data_ + length_, N - length_, format, ap);
        return *this;
    }

    // Gets the buffer's contents as a string.
    fbl::String ToString() const {
        return fbl::String(data(), length());
    }

    // Gets the buffer's contents as a string piece.
    fbl::StringPiece ToStringPiece() const {
        return fbl::StringPiece(data(), length());
    }

private:
    void AppendInternal(const char* data, size_t length) {
        size_t remaining = N - length_;
        if (length > remaining)
            length = remaining;
        memcpy(data_ + length_, data, length);
        length_ += length;
        data_[length_] = 0;
    }

    size_t length_ = 0u;
    char data_[N + 1u];
};

} // namespace fbl