HTTPサーバーを作ってみる

socket_programming/README.md

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+## ビルド実行方法
+```shell
+gcc -Wall -Wextra -o server server.c
+gcc -Wall -Wextra -o client client.c
+
+./server &  # サーバー起動
+
+# curl でテスト
+curl "http://localhost:8080/calc?query=2+10"  # → 12
+curl "http://localhost:8080/calc?query=3*4"   # → 12
+curl "http://localhost:8080/calc?query=10/0"  # → Bad Request
+
+# 自作クライアントでテスト
+➜  socket_programming git:(socket-programming) ✗ ./client "10+2"      
+HTTP/1.1 200 OK
+Content-Length: 2
+Content-Type: text/plain
+Connection: close
+
+12
+➜  socket_programming git:(socket-programming) ✗ ./client "10*2"
+HTTP/1.1 200 OK
+Content-Length: 2
+Content-Type: text/plain
+Connection: close
+
+20
+➜  socket_programming git:(socket-programming) ✗ ./client "10-2"
+HTTP/1.1 200 OK
+Content-Length: 1
+Content-Type: text/plain
+Connection: close
+
+8
+➜  socket_programming git:(socket-programming) ✗ ./client "10/0"
+HTTP/1.1 400 Bad Request
+Content-Length: 11
+Content-Type: text/plain
+Connection: close
+
+Bad Request
+➜  socket_programming git:(socket-programming) ✗ ./client "10/2"
+HTTP/1.1 200 OK
+Content-Length: 1
+Content-Type: text/plain
+Connection: close
+
+5
+
+
+## 対応OS
+- Mac / Linux (Ubuntu 等)
+- Windows は非対応 (unistd.h 等の POSIX ヘッダーが使用不可なため。対応するには Winsock に書き直す必要あり)

socket_programming/client.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netdb.h>
+
+#define HOST "127.0.0.1"
+#define PORT "8080"
+
+int main(int argc, char *argv[]) {
+    const char *expr = (argc > 1) ? argv[1] : "2+10";
+
+    struct addrinfo hints, *res;
+    memset(&hints, 0, sizeof hints);
+    hints.ai_family   = AF_UNSPEC;
+    hints.ai_socktype = SOCK_STREAM;
+
+    int rv = getaddrinfo(HOST, PORT, &hints, &res);
+    if (rv != 0) { fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv)); return 1; }
+
+    int sfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);
+    if (sfd < 0) { perror("socket"); return 1; }
+
+    if (connect(sfd, res->ai_addr, res->ai_addrlen) < 0) { perror("connect"); return 1; }
+    freeaddrinfo(res);
+
+    /* リクエスト送信 */
+    char req[512];
+    int reqlen = snprintf(req, sizeof req,
+        "GET /calc?query=%s HTTP/1.1\r\n"
+        "Host: localhost\r\n"
+        "Connection: close\r\n"
+        "\r\n",
+        expr);
+    write(sfd, req, reqlen);
+
+    /* レスポンス受信・表示 */
+    char buf[4096];
+    ssize_t n;
+    while ((n = read(sfd, buf, sizeof buf - 1)) > 0) {
+        buf[n] = '\0';
+        printf("%s", buf);
+    }
+    printf("\n");
+    close(sfd);
+    return 0;
+}

socket_programming/server.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netdb.h>
+#include <arpa/inet.h>
+
+#define PORT "8080"
+#define BACKLOG 10
+#define BUF_SIZE 4096
+
+/* -------------------------------------------------------
+ * /calc?query=<expression> を評価する
+ * 対応演算子: + - * /
+ * 返り値: 動的確保した結果文字列（呼び出し元が free する）
+ *         エラー時は NULL
+ * ------------------------------------------------------- */
+static char *calc(const char *query_string) {
+    /* query_string は "query=2+10" など */
+    const char *eq = strchr(query_string, '=');
+    if (!eq) return NULL;
+
+    const char *expr = eq + 1;   // const char*
+    printf("DEBUG expr: [%s]\n", expr);
+
+    double left, right;
+    char op;
+    if (sscanf(expr, " %lf %c %lf", &left, &op, &right) != 3) {
+        return NULL;  // free(expr) を削除
+    }
+
+    double result;
+    switch (op) {
+        case '+': result = left + right; break;
+        case '-': result = left - right; break;
+        case '*': result = left * right; break;
+        case '/':
+            if (right == 0) return NULL;
+            result = left / right;
+            break;
+        default: return NULL;
+    }
+
+    /* 整数なら整数表示、そうでなければ小数表示 */
+    char *buf = malloc(64);
+    if (!buf) { perror("malloc"); exit(1); }
+    if (result == (long long)result)
+        snprintf(buf, 64, "%lld", (long long)result);
+    else
+        snprintf(buf, 64, "%g", result);
+    return buf;
+}
+
+/* -------------------------------------------------------
+ * 1リクエストの処理
+ * ------------------------------------------------------- */
+static void handle_request(int fd) {
+    /* リクエスト全体を読む */
+    char *req = malloc(BUF_SIZE);
+    if (!req) { perror("malloc"); exit(1); }
+    ssize_t total = 0;
+    while (total < BUF_SIZE - 1) {
+        ssize_t n = read(fd, req + total, BUF_SIZE - 1 - total);
+        if (n < 0) { perror("read"); free(req); return; }
+        if (n == 0) break;
+        total += n;
+        /* ヘッダー終端 \r\n\r\n が来たら終了 */
+        req[total] = '\0';
+        if (strstr(req, "\r\n\r\n")) break;
+    }
+    req[total] = '\0';
+    printf("--- request ---\n%s\n", req);
+
+    /* リクエストライン解析: "GET /path?query HTTP/1.x" */
+    char method[16], path[1024], version[16];
+    if (sscanf(req, "%15s %1023s %15s", method, path, version) != 3) {
+        free(req);
+        return;
+    }
+    free(req);
+
+    /* パスとクエリ文字列に分割 */
+    char *qmark = strchr(path, '?');
+    char *query_string = NULL;
+    if (qmark) {
+        *qmark = '\0';
+        query_string = qmark + 1;
+    }
+
+    /* レスポンスボディ生成 */
+    char *body = NULL;
+    int status = 200;
+    const char *status_msg = "OK";
+
+    if (strcmp(method, "GET") == 0 && strcmp(path, "/calc") == 0 && query_string) {
+        body = calc(query_string);
+    }
+
+    if (!body) {
+        status = 400;
+        status_msg = "Bad Request";
+        body = strdup("Bad Request");
+        if (!body) { perror("strdup"); exit(1); }
+    }
+
+    /* レスポンス送信 */
+    size_t body_len = strlen(body);
+    char *header = malloc(256);
+    if (!header) { perror("malloc"); exit(1); }
+    int hlen = snprintf(header, 256,
+        "HTTP/1.1 %d %s\r\n"
+        "Content-Length: %zu\r\n"
+        "Content-Type: text/plain\r\n"
+        "Connection: close\r\n"
+        "\r\n",
+        status, status_msg, body_len);
+
+    /* ヘッダー */
+    ssize_t written = 0;
+    while (written < hlen) {
+        ssize_t n = write(fd, header + written, hlen - written);
+        if (n < 0) { perror("write"); break; }
+        written += n;
+    }
+    /* ボディ */
+    written = 0;
+    while ((size_t)written < body_len) {
+        ssize_t n = write(fd, body + written, body_len - written);
+        if (n < 0) { perror("write"); break; }
+        written += n;
+    }
+
+    free(header);
+    free(body);
+}
+
+/* -------------------------------------------------------
+ * サーバーソケット作成 (IPv4/IPv6 両対応)
+ * ------------------------------------------------------- */
+static int create_server_socket(void) {
+    struct addrinfo hints, *res, *p;
+    memset(&hints, 0, sizeof hints);
+    hints.ai_family   = AF_UNSPEC;    /* IPv4 / IPv6 どちらでも */
+    hints.ai_socktype = SOCK_STREAM;
+    hints.ai_flags    = AI_PASSIVE;   /* INADDR_ANY */
+
+    int rv = getaddrinfo(NULL, PORT, &hints, &res);
+    if (rv != 0) {
+        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
+        exit(1);
+    }
+
+    int sfd = -1;
+    for (p = res; p != NULL; p = p->ai_next) {
+        sfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
+        if (sfd < 0) { perror("socket"); continue; }
+
+        int yes = 1;
+        if (setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof yes) < 0) {
+            perror("setsockopt"); close(sfd); continue;
+        }
+
+        if (bind(sfd, p->ai_addr, p->ai_addrlen) < 0) {
+            perror("bind"); close(sfd); continue;
+        }
+        break; /* 成功 */
+    }
+    freeaddrinfo(res);
+
+    if (sfd < 0) {
+        fprintf(stderr, "failed to bind\n");
+        exit(1);
+    }
+
+    if (listen(sfd, BACKLOG) < 0) {
+        perror("listen"); exit(1);
+    }
+    return sfd;
+}
+
+/* -------------------------------------------------------
+ * main
+ * ------------------------------------------------------- */
+int main(void) {
+    int sfd = create_server_socket();
+    printf("Listening on port %s ...\n", PORT);
+
+    while (1) {
+        struct sockaddr_storage client_addr;
+        socklen_t addrlen = sizeof client_addr;
+        int cfd = accept(sfd, (struct sockaddr *)&client_addr, &addrlen);
+        if (cfd < 0) { perror("accept"); continue; }
+
+        /* クライアントの IP アドレスを表示 */
+        char ipstr[INET6_ADDRSTRLEN];
+        if (client_addr.ss_family == AF_INET) {
+            struct sockaddr_in *s = (struct sockaddr_in *)&client_addr;
+            inet_ntop(AF_INET, &s->sin_addr, ipstr, sizeof ipstr);
+        } else {
+            struct sockaddr_in6 *s = (struct sockaddr_in6 *)&client_addr;
+            inet_ntop(AF_INET6, &s->sin6_addr, ipstr, sizeof ipstr);
+        }
+        printf("Connection from %s\n", ipstr);
+
+        handle_request(cfd);
+        close(cfd);
+    }
+
+    close(sfd);
+    return 0;
+}