Implement primitive dictzip index queries

2 files changed, 69 insertions, 0 deletions

diff --git a/src/util/query.cc b/src/util/query.cc
new file mode 100644
index 0000000..a6fdcd3
--- /dev/null
+++ b/src/util/query.cc
@@ -0,0 +1,57 @@
+#include "query.h"
+
+#include <fcntl.h>
+
+#include <cstdio>
+#include <cstring>
+
+#include <stdexcept>
+
+namespace dictzip {
+
+std::string get_line_starting_with(
+	const std::string& path, const std::string& substring) {
+	static const auto BUFFER_SIZE = 16*1024;
+
+	FILE* file = std::fopen(path.c_str(), "r");
+
+	posix_fadvise(fileno(file), 0, 0, 1);  // FDADVICE_SEQUENTIAL
+
+	char buffer[BUFFER_SIZE + 1];
+	char* start_of_match = nullptr;
+
+	while( std::size_t bytes_read = std::fread(buffer, sizeof(char), BUFFER_SIZE, file) ) {
+		if ( bytes_read ) {
+			for ( char* p = buffer;
+			      (p = static_cast<char*>(std::memchr(p, '\n', (buffer + bytes_read) - p)));
+			      ++p ) {
+				if ( start_of_match == nullptr ) {
+					if ( std::strncmp(substring.c_str(), p+1, substring.size()) == 0 ) {
+						start_of_match = p+1;
+					}
+				} else {
+					return std::string(start_of_match, p-start_of_match);
+				}
+			}
+		} else {
+			break;
+		}
+	}
+
+	throw std::runtime_error("No match found");
+}
+
+std::string get_encoded_offset(const std::string& line) {
+	const std::size_t start = line.find_first_of('\t');
+	const std::size_t end   = line.find_last_of('\t');
+
+	return line.substr(start + 1, end - (start + 1));
+}
+
+std::string get_encoded_length(const std::string& line) {
+	const std::size_t start = line.find_last_of('\t');
+
+	return line.substr(start + 1);
+}
+
+}
diff --git a/src/util/query.h b/src/util/query.h
new file mode 100644
index 0000000..3a25206
--- /dev/null
+++ b/src/util/query.h
@@ -0,0 +1,12 @@
+#pragma once
+
+#include <string>
+
+namespace dictzip {
+
+std::string get_line_starting_with(const std::string& path, const std::string& substring);
+
+std::string get_encoded_offset(const std::string& line);
+std::string get_encoded_length(const std::string& line);
+
+}