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v0.1: release first version
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Diff for: ‎.gitignore

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build/

Diff for: ‎LICENSE

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Diff for: ‎README.md

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# libnss_docker
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*A NSS service for Docker containers resolving*
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:warning: *This is a **toy** project and has not been intensely tested! Use at your own risk*
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## Dependencies
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- `libcurl` (>= 7.80)
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- `libcjson` (>= 1.7.15)
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*Note that older versions of the dependencies may work, but they have not been tested*
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## Install
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Requires `meson` and `ninja`.
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```bash
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meson build && cd build && meson install
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```
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## Build
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Requires `meson` and `ninja`.
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```bash
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meson --buildtype=debug build && cd build && meson compile
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```

Diff for: ‎meson.build

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project(
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'nss-docker', 'c',
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version: '0.1',
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license: 'GPL-3.0-or-later',
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meson_version: '>=0.61.1',
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default_options: [
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'prefix=/usr',
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'buildtype=release',
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'warning_level=3',
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'werror=true',
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'b_lto=true',
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'b_lto_mode=thin',
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'b_ndebug=if-release',
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'strip=true' # only strip on install
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],
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)
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subdir('src')
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install_man('nss-docker.8')

Diff for: ‎nss-docker.8

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.TH NSS-DOCKER 8 2022-02-11 "nss-docker 0.1"
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.SH NAME
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nss-docker, libnss_docker\&.so\&.2 - Hostname resolution for Docker containers
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.SH DESCRIPTION
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.PP
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\fBnss-docker\fP is a plug-in module for the GNU Name Service Switch (NSS) functionality of the glibc providing hostname resolution for the names and UUID of Docker containers.
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.PP
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To use this module, add "docker" to the line starting with "hosts:" in the file /etc/nssswitch.conf.
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.SH EXAMPLE
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.PP
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Here is an example of /etc/nssswitch.conf with "docker" enabled:
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.PP
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.RS 4
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.EX
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passwd: files systemd
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group: files [SUCCESS=merge] systemd
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shadow: files systemd
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gshadow: files systemd
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publickey: files
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hosts: mymachines mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] files myhostname \fBdocker\fP dns
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networks: files
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protocols: files
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services: files
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ethers: files
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rpc: files
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netgroup: files
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.EE
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It is recommended to place "docker" at the end \fBbut before\fP "dns".
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.SH SEE ALSO
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.PP
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\fBnsswitch.conf\fP(5), \fBgetent\fP(1)
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.SH AUTHOR
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Kenji 'Nhqml' Gaillac

Diff for: ‎src/container.c

Whitespace-only changes.

Diff for: ‎src/container.h

Whitespace-only changes.

Diff for: ‎src/docker_api.c

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#include <errno.h>
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#include <error.h>
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#include <stdlib.h>
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#include <string.h>
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#include <cjson/cJSON.h>
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#include <curl/curl.h>
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#include "docker_api.h"
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#include "utils.h"
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size_t jsonify(void *data, size_t size, size_t nmemb, void *userdata)
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{
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size_t realsize = size * nmemb;
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struct cJSON *json = cJSON_Parse(data);
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*(struct cJSON **)userdata = json;
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return realsize;
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}
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char *_inspect_container_url(const char *name)
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{
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char *url = xmalloc(_DOCKER_API_URL_BASE_SIZE + strlen(name) + 1);
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sprintf(url, DOCKER_API_ENDPOINT DOCKER_API_VERSION DOCKER_API_URL_P1 "%s" DOCKER_API_URL_P2, name);
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return url;
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}
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struct container *container_new(const char *name)
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{
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struct container *container = xmalloc(sizeof(struct container));
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size_t name_len = strlen(name);
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container->name = xmalloc(name_len + 1);
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strcpy(container->name, name);
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container->short_uuid = xmalloc(DOCKER_SHORT_UUID_SIZE + 1);
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container->addr_list = xcalloc(1, sizeof(char *));
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container->n_addr = 0;
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return container;
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}
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struct container *container_set_short_uuid(struct container *container, const char *uuid)
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{
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strncpy(container->short_uuid, uuid, DOCKER_SHORT_UUID_SIZE);
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container->short_uuid[DOCKER_SHORT_UUID_SIZE] = '\0';
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return container;
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}
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struct container *container_add_addr(struct container *container, char *addr)
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{
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if (addr != NULL)
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{
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++container->n_addr;
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container->addr_list = xreallocarray(container->addr_list, container->n_addr + 1, sizeof(char *));
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container->addr_list[container->n_addr - 1] = addr;
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container->addr_list[container->n_addr] = NULL;
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}
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return container;
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}
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void container_free(struct container *container)
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{
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if (container != NULL)
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{
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free(container->name);
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free(container->short_uuid);
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for (char **addr = container->addr_list; *addr != NULL; ++addr)
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free(*addr);
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free(container->addr_list);
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free(container);
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}
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}
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struct container *inspect_container(const char *name, int af)
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{
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CURL *curl = curl_easy_init();
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if (curl == NULL)
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error(1, errno, "failed when trying to retrieve containers");
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struct curl_slist *headers = curl_slist_append(NULL, "Accept: application/json");
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headers = curl_slist_append(headers, "Content-Type: application/json; charset=utf-8");
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curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
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curl_easy_setopt(curl, CURLOPT_UNIX_SOCKET_PATH, DOCKER_API_SOCK);
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char *docker_api_url = _inspect_container_url(name);
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curl_easy_setopt(curl, CURLOPT_URL, docker_api_url);
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struct cJSON *json;
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curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, jsonify);
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curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&json);
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CURLcode res = curl_easy_perform(curl);
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if (res != CURLE_OK)
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error(1, 0, "failed when trying to retrieve containers: %s", curl_easy_strerror(res));
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long http_code = 0;
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curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &http_code);
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free(docker_api_url);
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curl_easy_cleanup(curl);
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if (http_code != 200)
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return NULL;
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struct container *container = NULL;
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struct cJSON *container_name = cJSON_GetObjectItemCaseSensitive(json, "Name");
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if (!cJSON_IsString(container_name))
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return NULL;
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container = container_new(container_name->valuestring + 1); // +1 to skip leading '/' in the name
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struct cJSON *container_uuid = cJSON_GetObjectItemCaseSensitive(json, "Id");
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if (cJSON_IsString(container_uuid))
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container_set_short_uuid(container, container_uuid->valuestring);
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struct cJSON *container_netsettings = cJSON_GetObjectItemCaseSensitive(json, "NetworkSettings");
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if (container_netsettings != NULL)
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{
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struct cJSON *container_nets = cJSON_GetObjectItemCaseSensitive(container_netsettings, "Networks");
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for (int i = 0; i < cJSON_GetArraySize(container_nets); ++i)
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{
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struct cJSON *container_net = cJSON_GetArrayItem(container_nets, i);
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if (container_net != NULL)
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{
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char *container_addr = cJSON_GetStringValue(cJSON_GetObjectItemCaseSensitive(container_net, "IPAddress"));
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if (container_addr != NULL && container_addr[0] != '\0')
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container_add_addr(container, parse_addr(container_addr, af));
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}
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}
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}
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cJSON_free(json);
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if (container->n_addr == 0)
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{
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container_free(container);
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container = NULL;
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}
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return container;
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}

Diff for: ‎src/docker_api.h

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#pragma once
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#define DOCKER_API_SOCK "/var/run/docker.sock"
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#define DOCKER_API_ENDPOINT "http://localhost/"
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#define DOCKER_API_VERSION "v1.41"
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#define DOCKER_API_URL_P1 "/containers/"
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#define DOCKER_API_URL_P2 "/json"
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#define _DOCKER_API_URL_BASE_SIZE 39
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#define DOCKER_UUID_SIZE 64
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#define DOCKER_SHORT_UUID_SIZE 12
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#define DOCKER_LOCAL_DOMAIN ".docker.local"
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struct container
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{
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char *name;
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char *short_uuid;
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size_t n_addr;
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char **addr_list;
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};
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struct container *inspect_container(const char *name, int af);

Diff for: ‎src/docker_nss.c

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#include <arpa/inet.h>
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#include <netdb.h>
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#include <nss.h>
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#include <string.h>
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#include "docker_api.h"
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#include "docker_nss.h"
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#include "utils.h"
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enum nss_status _nss_docker_gethostbyname_r(const char *name,
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struct hostent *result,
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char *buf, size_t buflen,
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int *errnop, int *h_errnop)
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{
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return _nss_docker_gethostbyname3_r(name, AF_INET, result, buf, buflen, errnop, h_errnop, NULL, NULL);
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}
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enum nss_status _nss_docker_gethostbyname2_r(const char *name, int af,
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struct hostent *result,
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char *buf, size_t buflen,
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int *errnop, int *h_errnop)
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{
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return _nss_docker_gethostbyname3_r(name, af, result, buf, buflen, errnop, h_errnop, NULL, NULL);
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}
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/**
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** \brief Returns the name without docker local domain
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*/
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char *strip_docker_local_domain(const char *name)
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{
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if (name == NULL)
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return NULL;
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char *stripped_name = xstrdup(name);
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for (char *c = stripped_name; *c != '\0'; ++c)
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{
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if (*c == '.')
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{
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if (strcmp(c, DOCKER_LOCAL_DOMAIN) == 0)
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{
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*c = '\0'; // Terminate the string here
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break;
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}
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}
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}
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return stripped_name;
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}
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enum nss_status _nss_docker_gethostbyname3_r(const char *name, int af,
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struct hostent *result,
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char *buf, size_t buflen,
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int *errnop, int *h_errnop,
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int32_t *ttlp, char **canonp)
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{
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/* I don't know for sure what ttlp is, my guess is that it's a pointer to
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the TTL but since it's seems that no one uses it, neither am I... */
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if (ttlp)
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*ttlp = 0;
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if (af == AF_UNSPEC)
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af = AF_INET;
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(void)buf;
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(void)buflen;
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char *stripped_name = strip_docker_local_domain(name);
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struct container *container = inspect_container(stripped_name, af);
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free(stripped_name);
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if (container == NULL)
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return NSS_STATUS_NOTFOUND;
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char **r_aliases = xcalloc(2, sizeof(char *));
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r_aliases[0] = container->short_uuid;
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result->h_name = container->name;
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result->h_aliases = r_aliases;
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result->h_addrtype = af;
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result->h_length = 4;
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result->h_addr_list = container->addr_list;
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*errnop = 0;
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*h_errnop = 0;
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/* I don't know for sure what canonp is, my guess is that it's a pointer to
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a list of "canonical names" */
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if (canonp)
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*canonp = result->h_name;
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return NSS_STATUS_SUCCESS;
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}

Diff for: ‎src/docker_nss.h

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#pragma once
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#define PUBLIC __attribute__((visibility("default")))
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#define MAX_NR_ALIASES 48
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#define MAX_NR_ADDRS 48
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#include <nss.h>
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enum nss_status
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PUBLIC
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_nss_docker_gethostbyname_r(const char *name,
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struct hostent *result,
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char *buf, size_t buflen,
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int *errnop, int *h_errnop);
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enum nss_status
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PUBLIC
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_nss_docker_gethostbyname2_r(const char *name, int af,
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struct hostent *result,
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char *buf, size_t buflen,
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int *errnop, int *h_errnop);
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enum nss_status
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PUBLIC
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_nss_docker_gethostbyname3_r(const char *name, int af,
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struct hostent *result,
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char *buf, size_t buflen,
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int *errnop, int *h_errnop,
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int32_t *ttlp, char **canonp);

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