README.md: Update according to thumbnail generation

This new application runs separately from slcl and communicates with it
via a named pipe. When files are added/removed to/from the user
directory, slcl shall write to the named pipe.

Then, this new tool shall process incoming entries and generate
or remove thumbnails accordingly. Such thumbnails are stored into a new
directory inside the database directory, namely thumbnails/, which
replicates the same structure as user/.

.gitignore

@@ -1,5 +1,6 @@
 build/
 slcl
+thumbnail/thumbnail
 *.o
 *.d
 ./Makefile

README.md

@@ -23,6 +23,9 @@ portability, minimalism, simplicity and efficiency.
 - Uses [`libweb`](https://gitea.privatedns.org/xavi/libweb), a tiny web framework.
 - A simple JSON file as the credentials database.
 - No JavaScript.
+- Thumbnail generation can be optionally provided via a
+[separate application](thumbnail/README-md) and enabled by `slcl` via a command
+line option. Inter-process communication is achieved via a named pipe.
 
 ### TLS
 
@@ -123,16 +126,32 @@ anything users put into them.
 
 **Note:** `slcl` creates the given directory if it does not exist.
 
+[Generated thumbnails](thumbnail/README.md) are stored into another directory,
+namely `thumbnails`, which is automatically created with directory mode bits
+set to `0700`.
+
+```
+.
+├── db.json
+├── public
+├── thumbnails
+└── user
+```
+
 A more complete example:
 
 ```
 .
 ├── db.json
 ├── public
-│   └── 44e03ab1bc3b0eff1567c76619186596 -> user/alice/file.txt
+│   └── 44e03ab1bc3b0eff1567c76619186596 -> user/alice/file.jpg
+├── thumbnails
+│   ├── alice
+│   │   └── file.jpg
+│   └── john
 └── user
     ├── alice
-    │   └── file.txt
+    │   └── file.jpg
     └── john
         └── file2.txt
 ```
@@ -199,6 +218,16 @@ temporary directory to the database, which might be an expensive operation.
 Therefore, in order to avoid expensive copies, define a custom temporary
 directory that resides on the same filesystem.
 
+#### Thumbnail generation and rendering
+
+Optionally, `slcl` displays thumbnails when listing a directory, if available
+from the `thumbnails/` directory. In order to update these thumbnails when
+files are added/removed to/from the database, a separate application must be
+executed. See its [`README.md`](thumbnail/README.md) for further reference.
+
+`slcl` provides the `-F` command line option to enable the use of a named pipe
+that shall be used by the [thumbnail generation tool](thumbnail/).
+
 ## Why this project?
 
 Previously, I had been recommended Nextcloud as an alternative to proprietary

main.c

@@ -710,10 +710,14 @@ static int search(const struct http_payload *const p,
     const struct user_args *const args = user;
     const struct auth *const a = args->a;
     const char *const username = p->cookie.field, *const root = auth_dir(a);
-    struct page_search s = {0};
     int (*f)(struct http_response *);
     char *dir = NULL;
     struct dynstr userd, d, res;
+    struct page_search s =
+    {
+        .username = username,
+        .adir = root
+    };
 
     dynstr_init(&userd);
     dynstr_init(&d);
@@ -990,6 +994,8 @@ static int getnode(const struct http_payload *const p,
         .r = r,
         .args = p->args,
         .n_args = p->n_args,
+        .username = username,
+        .adir = adir,
         .dir = dir.str,
         .root = root.str,
         .res = d.str,
@@ -2011,6 +2017,55 @@ end:
     return ret;
 }
 
+static int getthumbnail(const struct http_payload *const p,
+    struct http_response *const r, void *const user)
+{
+    int ret = -1;
+    const struct user_args *const ua = user;
+    const struct auth *const a = ua->a;
+    struct dynstr d, dir;
+
+    dynstr_init(&d);
+    dynstr_init(&dir);
+
+    if (auth_cookie(a, &p->cookie))
+    {
+        fprintf(stderr, "%s: auth_cookie failed\n", __func__);
+        ret = page_forbidden(r);
+        goto end;
+    }
+
+    const char *const adir = auth_dir(a);
+
+    if (!adir)
+    {
+        fprintf(stderr, "%s: auth_dir failed\n", __func__);
+        goto end;
+    }
+    else if (dynstr_append(&d, "%s%s", adir, p->resource))
+    {
+        fprintf(stderr, "%s: dynstr_append failed\n", __func__);
+        goto end;
+    }
+    else if (dynstr_dup(&dir, &d))
+    {
+        fprintf(stderr, "%s: dynstr_dup failed\n", __func__);
+        goto end;
+    }
+    else if (page_thumbnail(r, d.str))
+    {
+        fprintf(stderr, "%s: page_public failed\n", __func__);
+        goto end;
+    }
+
+    ret = 0;
+
+end:
+    dynstr_free(&d);
+    dynstr_free(&dir);
+    return ret;
+}
+
 static void usage(char *const argv[])
 {
     fprintf(stderr, "%s [-F] [-t tmpdir] [-p port] dir\n", *argv);
@@ -2243,7 +2298,8 @@ static int add_urls(struct handler *const h, void *const user)
         {.url = "/upload", .op = HTTP_OP_POST, .f = upload},
         {.url = "/mkdir", .op = HTTP_OP_POST, .f = createdir},
         {.url = "/confirm/rm", .op = HTTP_OP_POST, .f = confirm_rm},
-        {.url = "/rm", .op = HTTP_OP_POST, .f = rm}
+        {.url = "/rm", .op = HTTP_OP_POST, .f = rm},
+        {.url = "/thumbnails/*", .op = HTTP_OP_GET, .f = getthumbnail}
     };
 
     for (size_t i = 0; i < sizeof urls / sizeof *urls; i++)

page.c

@@ -101,6 +101,67 @@ end:
     return ret;
 }
 
+static int prepare_thumbnail(struct html_node *const n,
+    const struct stat *const sb, const struct page_resource *const pr,
+    const char *const name, const char *const sep)
+{
+    int ret = -1;
+    struct html_node *img;
+    struct dynstr abs, rel;
+    struct stat tsb;
+
+    dynstr_init(&abs);
+    dynstr_init(&rel);
+
+    if (!S_ISREG(sb->st_mode))
+    {
+        ret = 0;
+        goto end;
+    }
+    else if (!pr->adir || !pr->username)
+    {
+        ret = 0;
+        goto end;
+    }
+    else if (dynstr_append(&rel, "/thumbnails/%s%s%s%s",
+        pr->username, pr->dir + strlen("/user"), sep, name))
+    {
+        fprintf(stderr, "%s: dynstr_append rel failed\n", __func__);
+        goto end;
+    }
+    else if (dynstr_append(&abs, "%s%s", pr->adir, rel.str))
+    {
+        fprintf(stderr, "%s: dynstr_append rel failed\n", __func__);
+        goto end;
+    }
+    else if (stat(abs.str, &tsb))
+    {
+        if (errno == ENOENT)
+            ret = 0;
+        else
+            fprintf(stderr, "%s: stat(2): %s\n", __func__, strerror(errno));
+
+        goto end;
+    }
+    else if (!(img = html_node_add_child(n, "img")))
+    {
+        fprintf(stderr, "%s: html_node_add_child failed\n", __func__);
+        goto end;
+    }
+    else if (html_node_add_attr(img, "src", rel.str))
+    {
+        fprintf(stderr, "%s: html_node_add_attr src failed\n", __func__);
+        goto end;
+    }
+
+    ret = 0;
+
+end:
+    dynstr_free(&abs);
+    dynstr_free(&rel);
+    return ret;
+}
+
 static int prepare_name(struct html_node *const n, struct stat *const sb,
     const char *const dir, const char *const name)
 {
@@ -338,19 +399,19 @@ end:
     return ret;
 }
 
-static int add_element(struct html_node *const n, const char *const dir,
-    const char *const res, const char *const name, const bool chbx,
-    struct element_stats *const st)
+static int add_element(struct html_node *const n,
+    const struct page_resource *const pr, const char *const name,
+    const bool chbx, struct element_stats *const st)
 {
     int ret = -1;
-    enum {RM_CHECKBOX, NAME, SIZE, DATE, SHARE, PREVIEW, COLUMNS};
+    enum {RM_CHECKBOX, THUMBNAIL, NAME, SIZE, DATE, SHARE, PREVIEW, COLUMNS};
     struct html_node *tr, *td[COLUMNS];
     struct dynstr path;
-    const char *const sep = res[strlen(res) - 1] != '/' ? "/" : "";
+    const char *const sep = pr->res[strlen(pr->res) - 1] != '/' ? "/" : "";
 
     dynstr_init(&path);
 
-    if (dynstr_append(&path, "%s%s%s", res, sep, name))
+    if (dynstr_append(&path, "%s%s%s", pr->res, sep, name))
     {
         fprintf(stderr, "%s: dynstr_append failed\n", __func__);
         goto end;
@@ -392,7 +453,12 @@ static int add_element(struct html_node *const n, const char *const dir,
         fprintf(stderr, "%s: prepare_rm_checkbox failed\n", __func__);
         goto end;
     }
-    else if (prepare_name(td[NAME], &sb, dir, name))
+    else if (prepare_thumbnail(td[THUMBNAIL], &sb, pr, name, sep))
+    {
+        fprintf(stderr, "%s: prepare_thumbnail failed\n", __func__);
+        goto end;
+    }
+    else if (prepare_name(td[NAME], &sb, pr->dir, name))
     {
         fprintf(stderr, "%s: prepare_name failed\n", __func__);
         goto end;
@@ -407,12 +473,12 @@ static int add_element(struct html_node *const n, const char *const dir,
         fprintf(stderr, "%s: prepare_date failed\n", __func__);
         goto end;
     }
-    else if (prepare_share(td[SHARE], &sb, dir, name))
+    else if (prepare_share(td[SHARE], &sb, pr->dir, name))
     {
         fprintf(stderr, "%s: prepare_date failed\n", __func__);
         goto end;
     }
-    else if (prepare_preview(td[PREVIEW], &sb, dir, name))
+    else if (prepare_preview(td[PREVIEW], &sb, pr->dir, name))
     {
         fprintf(stderr, "%s: prepare_date failed\n", __func__);
         goto end;
@@ -1129,13 +1195,12 @@ end:
     return ret;
 }
 
-static int add_elements(const char *const root, const char *const res,
-    const char *const dir, struct html_node *const table,
-    struct element_stats *const st)
+static int add_elements(const struct page_resource *const pr,
+    struct html_node *const table, struct element_stats *const st)
 {
     int ret = -1;
     struct dirent **pde = NULL;
-    const int n = scandir(res, &pde, NULL, alphasort);
+    const int n = scandir(pr->res, &pde, NULL, alphasort);
 
     if (n < 0)
     {
@@ -1151,9 +1216,9 @@ static int add_elements(const char *const root, const char *const res,
         const char *const name = de->d_name;
 
         if (!strcmp(name, ".")
-            || (!strcmp(name, "..") && !strcmp(root, res)))
+            || (!strcmp(name, "..") && !strcmp(pr->root, pr->res)))
             continue;
-        else if (add_element(table, dir, res, name, true, st))
+        else if (add_element(table, pr, name, true, st))
         {
             fprintf(stderr, "%s: add_element failed\n", __func__);
             goto end;
@@ -1220,7 +1285,7 @@ static int list_dir(const struct page_resource *const pr)
         fprintf(stderr, "%s: resource_layout failed\n", __func__);
         goto end;
     }
-    else if (add_elements(pr->root, pr->res, pr->dir, table, &st))
+    else if (add_elements(pr, table, &st))
     {
         fprintf(stderr, "%s: read_elements failed\n", __func__);
         goto end;
@@ -1815,8 +1880,15 @@ static int add_search_results(struct html_node *const n,
     for (size_t i = 0; i < s->n; i++)
     {
         const struct page_search_result *const r = &s->results[i];
+        const struct page_resource pr =
+        {
+            .dir = "/user/",
+            .adir = s->adir,
+            .username = s->username,
+            .res = s->root
+        };
 
-        if (add_element(table, "/user/", s->root, r->name, false, NULL))
+        if (add_element(table, &pr, r->name, false, NULL))
         {
             fprintf(stderr, "%s: add_element failed\n", __func__);
             return -1;
@@ -2232,3 +2304,30 @@ int page_head_resource(struct http_response *const r, const char *const res)
 
     return 0;
 }
+
+int page_thumbnail(struct http_response *const r, const char *const res)
+{
+    struct stat sb;
+
+    if (stat(res, &sb))
+    {
+        if (errno == ENOENT)
+            return page_not_found(r);
+        else
+        {
+            fprintf(stderr, "%s: stat(2) %s: %s\n",
+                __func__, res, strerror(errno));
+            return -1;
+        }
+    }
+
+    const mode_t m = sb.st_mode;
+
+    if (!S_ISREG(m))
+    {
+        fprintf(stderr, "%s: only regular files are supported\n", __func__);
+        return 1;
+    }
+
+    return serve_file(r, &sb, res, true);
+}

page.h

@@ -13,7 +13,7 @@ struct page_quota
 struct page_resource
 {
     struct http_response *r;
-    const char *dir, *root, *res;
+    const char *adir, *username, *dir, *root, *res;
     const struct page_quota *q;
     const struct http_arg *args;
     size_t n_args;
@@ -26,7 +26,7 @@ struct page_search
         char *name;
     } *results;
 
-    const char *root;
+    const char *root, *adir, *username;
     size_t n;
     bool limit_exceeded;
 };
@@ -50,5 +50,6 @@ int page_quota_exceeded(struct http_response *r, unsigned long long len,
     unsigned long long quota);
 int page_search(struct http_response *r, const struct page_search *s);
 int page_rm(struct http_response *r, const struct page_rm *rm);
+int page_thumbnail(struct http_response *r, const char *res);
 
 #endif /* PAGE_H */

thumbnail/CMakeLists.txt

@@ -0,0 +1,10 @@
+cmake_minimum_required(VERSION 3.13)
+project(thumbnail)
+add_executable(${PROJECT_NAME} cftw.c crealpath.c main.c)
+add_subdirectory(${CMAKE_CURRENT_LIST_DIR}/../libweb/dynstr
+    ${CMAKE_BINARY_DIR}/dynstr)
+target_include_directories(${PROJECT_NAME} PRIVATE ..)
+target_compile_definitions(${PROJECT_NAME} PRIVATE _FILE_OFFSET_BITS=64)
+include(FindPkgConfig)
+pkg_check_modules(ImageMagick REQUIRED IMPORTED_TARGET ImageMagick)
+target_link_libraries(${PROJECT_NAME} PRIVATE dynstr PkgConfig::ImageMagick)

thumbnail/Makefile

@@ -0,0 +1,29 @@
+.POSIX:
+
+PROJECT = thumbnail
+O = -Og
+CDEFS = -D_FILE_OFFSET_BITS=64 # Required for large file support on 32-bit.
+CFLAGS = $(O) $(CDEFS) -g -Wall -I../libweb/dynstr/include -I. \
+	$$(pkg-config --cflags ImageMagick) -MD -MF $(@:.o=.d)
+LDFLAGS = $(LIBS)
+DEPS = $(OBJECTS:.o=.d)
+DYNSTR = ../libweb/dynstr/libdynstr.a
+DYNSTR_LIBS = -L../libweb/dynstr -ldynstr
+LIBS = $$(pkg-config --libs ImageMagick) $(DYNSTR_LIBS)
+OBJECTS = \
+	crealpath.o \
+	main.o \
+	cftw.o
+
+all: $(PROJECT)
+
+clean:
+	rm -f $(OBJECTS) $(DEPS)
+
+$(PROJECT): $(OBJECTS) $(DYNSTR)
+	$(CC) $(OBJECTS) $(LDFLAGS) $(LIBS) -o $@
+
+$(DYNSTR):
+	+cd ../dynstr && $(MAKE)
+
+-include $(DEPS)

thumbnail/README.md

@@ -0,0 +1,66 @@
+# Thumbnail generation tool for `slcl`
+
+This directory defines a separation application to be used in conjunction with
+`slcl`, aimed to update the thumbnail database automatically whenever files
+are added/removed to/from the database.
+
+### Root permissions
+
+This application requires no `root` permissions. So, in order to avoid the
+risk for security bugs, **please do not run this application as `root`**.
+
+## Requirements
+
+- A POSIX environment.
+- [`dynstr`](https://gitea.privatedns.org/xavi92/dynstr)
+(provided as a `git` submodule).
+- MagickCore
+- CMake (optional).
+
+### Ubuntu / Debian
+
+#### Mandatory packages
+
+```sh
+sudo apt install build-essential libmagickcore-6.q16-dev
+```
+
+#### Optional packages
+
+```sh
+sudo apt install cmake
+```
+
+## How to use
+### Build
+
+Similarly to `slcl`, two build environments are provided - feel free to choose
+any of them:
+
+- A mostly POSIX-compliant [`Makefile`](Makefile).
+- A [`CMakeLists.txt`](CMakeLists.txt).
+
+`thumbnail` can be built using the standard build process:
+
+#### Make
+
+```sh
+$ make
+```
+
+#### CMake
+
+```sh
+$ mkdir build/
+$ cmake ..
+$ cmake --build .
+```
+
+## Usage
+
+This tool only consumes one argument: the directory containing the instance
+database, which must be the same used by `slcl`. For example:
+
+```sh
+thumbnail ~/my-db
+```

thumbnail/cftw.c

@@ -0,0 +1 @@
+../cftw.c

thumbnail/cftw.h

@@ -0,0 +1 @@
+../cftw.h

thumbnail/crealpath.c

@@ -0,0 +1 @@
+../crealpath.c

thumbnail/crealpath.h

@@ -0,0 +1 @@
+../crealpath.h

thumbnail/main.c

@@ -0,0 +1,758 @@
+#define _POSIX_C_SOURCE 200809L
+
+#include "crealpath.h"
+#include <cftw.h>
+#include <dynstr.h>
+#include <magick/api.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <strings.h>
+#include <ctype.h>
+#include <errno.h>
+#include <limits.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static int print_error(const char *const func, const char *const ifunc,
+    const ExceptionInfo *const exc)
+{
+    const char *const reason = exc->reason ? exc->reason : "n/a",
+        *const description = exc->description ?
+            exc->description : "n/a";
+
+    return fprintf(stderr, "%s: %s failed: reason: %s, description: %s\n",
+        func, ifunc, reason, description);
+}
+
+static int create_thumbnail(const char *const src, const char *const dst,
+    const unsigned long size)
+{
+    int ret = -1;
+    const size_t slen = strlen(src), dlen = strlen(dst);
+    ImageInfo *info = NULL;
+    Image *i = NULL, *t = NULL;
+    ExceptionInfo *const exc = AcquireExceptionInfo();
+    /* Ensure permissions for files created by MagickCore.*/
+    const mode_t mode = umask(~(S_IRUSR | S_IWUSR));
+
+    if (slen >= sizeof i->filename)
+    {
+        fprintf(stderr, "%s: src maximum length exceeded (%zu, max %zu)\n",
+            __func__, slen, sizeof i->filename - 1);
+        goto end;
+    }
+    else if (dlen >= sizeof t->filename)
+    {
+        fprintf(stderr, "%s: dst maximum length exceeded (%zu, max %zu)\n",
+            __func__, slen, sizeof t->filename - 1);
+        goto end;
+    }
+    else if (!(info = CloneImageInfo(NULL)))
+    {
+        fprintf(stderr, "%s: CloneImageInfo failed\n", __func__);
+        goto end;
+    }
+
+    strcpy(info->filename, src);
+    info->adjoin = MagickTrue;
+
+    if (!(i = ReadImage(info, exc)))
+    {
+        switch (exc->severity)
+        {
+            case DelegateError:
+            case CorruptImageError:
+            case FileOpenError:
+            case MissingDelegateError:
+                ret = 1;
+                break;
+
+            default:
+                print_error(__func__, "ReadImage", exc);
+                break;
+        }
+
+        goto end;
+    }
+
+    if (!i->rows || !i->columns)
+    {
+        ret = 1;
+        goto end;
+    }
+
+    unsigned long x, y;
+
+    if (i->columns > i->rows)
+    {
+        x = i->columns > size ? size : i->columns;
+        y = x * i->rows / i->columns
+    }
+    else
+    {
+        y = i->rows > size ? size : i->rows;
+        x = y * i->columns / i->rows;
+    }
+
+    if (!(t = ResizeImage(i, x, y, PointFilter, 1, exc)))
+    {
+        print_error(__func__, "ResizeImage", exc);
+        goto end;
+    }
+    else if (WriteImages(info, t, dst, exc) != MagickTrue)
+    {
+        print_error(__func__, "WriteImages", exc);
+        goto end;
+    }
+
+    printf("Created %s\n", dst);
+    ret = 0;
+
+end:
+    umask(mode);
+
+    if (info)
+        DestroyImageInfo(info);
+
+    if (i)
+        DestroyImage(i);
+
+    if (t)
+        DestroyImage(t);
+
+    if (exc)
+        DestroyExceptionInfo(exc);
+
+    return ret;
+}
+
+static char *fifo_getline(const int fd)
+{
+    char *ret = NULL;
+    size_t n = 0;
+
+    for (;;)
+    {
+        char c;
+        ssize_t sz;
+
+again:
+        sz = read(fd, &c, sizeof c);
+
+        if (sz < 0)
+        {
+            if (errno == EAGAIN || errno == EINTR)
+                goto again;
+            else
+                fprintf(stderr, "%s: read(2): %s\n", __func__, strerror(errno));
+
+            goto failure;
+        }
+        else if (c == '\n')
+            break;
+
+        char *const aux = realloc(ret, n + 1);
+
+        if (!aux)
+        {
+            fprintf(stderr, "%s: realloc(3): %s\n",
+                __func__, strerror(errno));
+            goto failure;
+        }
+
+        aux[n++] = c;
+        ret = aux;
+    }
+
+    char *const aux = realloc(ret, n + 1);
+
+    if (!aux)
+    {
+        fprintf(stderr, "%s: realloc(3): %s\n", __func__, strerror(errno));
+        goto failure;
+    }
+
+    aux[n++] = '\0';
+    ret = aux;
+    return ret;
+
+failure:
+    free(ret);
+    return NULL;
+}
+
+static int ensure_dir(const char *const path, const size_t len)
+{
+    int ret = -1;
+    struct dynstr d;
+    struct stat sb;
+
+    dynstr_init(&d);
+
+    if (dynstr_append(&d, "%.*s", (int)len, path))
+    {
+        fprintf(stderr, "%s: dynstr_append failed\n", __func__);
+        goto end;
+    }
+    else if (stat(d.str, &sb))
+    {
+        if (errno != ENOENT && errno != ENOTDIR)
+        {
+            fprintf(stderr, "%s: stat(2) %s: %s\n",
+                __func__, d.str, strerror(errno));
+            goto end;
+        }
+        else if (mkdir(d.str, S_IRWXU))
+        {
+            fprintf(stderr, "%s: mkdir(2): %s\n", __func__, strerror(errno));
+            goto end;
+        }
+    }
+
+    ret = 0;
+
+end:
+    dynstr_free(&d);
+    return ret;
+}
+
+static int ensure_dirs(const char *const path)
+{
+    for (const char *p = path; p; p = strchr(p, '/'))
+    {
+        const char *const next = p + 1;
+
+        if (*next == '/')
+        {
+            p = next;
+            continue;
+        }
+        else if (!*next)
+        {
+            fprintf(stderr, "%s: expected file path: %s\n", __func__, path);
+            return 1;
+        }
+        else if (!(p = strchr(next, '/')))
+            break;
+        else if (ensure_dir(path, p - path))
+        {
+            fprintf(stderr, "%s: ensure_dir failed\n", __func__);
+            return -1;
+        }
+
+        p = next;
+    }
+
+    return 0;
+}
+
+static bool extension_allowed(const char *const path)
+{
+    static const char *const extensions[] =
+    {
+        ".jpg", ".jpeg", ".png", ".bmp"
+    };
+
+    for (size_t i = 0; i < sizeof extensions / sizeof *extensions; i++)
+    {
+        const char *const ext = extensions[i];
+        const size_t len = strlen(path), elen = strlen(ext);
+
+        if (len < elen)
+            continue;
+        else if (!strcasecmp(path + len - elen, ext))
+            return true;
+    }
+
+    return false;
+}
+
+static int process_add(const char *const abspath, const char *const relpath,
+    const char *const user, const char *const thumbnail,
+    const unsigned long size)
+{
+    int ret = -1;
+    struct dynstr d;
+
+    dynstr_init(&d);
+
+    if (!extension_allowed(abspath))
+        ;
+    else if (dynstr_append(&d, "%s%s", thumbnail, relpath))
+    {
+        fprintf(stderr, "%s: dynstr_append failed\n", __func__);
+        goto end;
+    }
+    else if ((ret = ensure_dirs(d.str)))
+    {
+        fprintf(stderr, "%s: ensure_dirs failed\n", __func__);
+        goto end;
+    }
+    else if ((ret = create_thumbnail(abspath, d.str, size)))
+    {
+        if (ret < 0)
+            fprintf(stderr, "%s: create_thumbnail failed\n", __func__);
+
+        goto end;
+    }
+
+    ret = 0;
+
+end:
+    dynstr_free(&d);
+    return ret;
+}
+
+static int process_rm(const char *const abspath, const char *const relpath,
+    const char *const user, const char *const thumbnail,
+    const unsigned long size)
+{
+    int ret = -1;
+    struct dynstr d;
+
+    dynstr_init(&d);
+
+    if (dynstr_append(&d, "%s%s", thumbnail, relpath))
+    {
+        fprintf(stderr, "%s: dynstr_append failed\n", __func__);
+        goto end;
+    }
+    else if (remove(d.str) && errno != ENOENT && errno != ENOTDIR)
+    {
+        fprintf(stderr, "%s: remove(3) %s: %s\n",
+            __func__, d.str, strerror(errno));
+        goto end;
+    }
+    else
+        printf("Removed %s\n", d.str);
+
+    ret = 0;
+
+end:
+    dynstr_free(&d);
+    return ret;
+}
+
+static int process_line(const char *const line, const char *const user,
+    const char *const thumbnail, const unsigned long size)
+{
+    int ret = -1;
+    const char *p = line;
+    static const char template[] = "+ f";
+    const size_t len = strlen(p);
+
+    if (len < strlen(template))
+    {
+        fprintf(stderr, "%s: invalid input: %s\n", __func__, p);
+        ret = 1;
+        goto end;
+    }
+
+    int (*f)(const char *, const char *, const char *, const char *,
+        unsigned long) = NULL;
+
+    switch (*p)
+    {
+        case '+':
+            f = process_add;
+            break;
+
+        case '-':
+            f = process_rm;
+            break;
+
+        default:
+            fprintf(stderr, "%s: unexpected operator %c\n", __func__, *p);
+            ret = 1;
+            goto end;
+    }
+
+    if (!isspace(*++p))
+    {
+        fprintf(stderr, "%s: expected whitespace: %s\n", __func__, line);
+        ret = 1;
+        goto end;
+    }
+
+    while (isspace(*p))
+        p++;
+
+    if (!*p)
+    {
+        fprintf(stderr, "%s: expected path: %s\n", __func__, line);
+        ret = 1;
+        goto end;
+    }
+
+    const char *const path = p, *rel;
+
+    if (strstr(path, user) != path)
+    {
+        fprintf(stderr, "%s: expected user directory (%s): %s\n",
+            __func__, user, line);
+        ret = 1;
+        goto end;
+    }
+
+    rel = path + strlen(user);
+
+    if ((ret = f(path, rel, user, thumbnail, size)) < 0)
+        fprintf(stderr, "%s: callback failed\n", __func__);
+
+end:
+    return ret;
+}
+
+static int process_input(const int fd, const char *const user,
+    const char *const thumbnail, const unsigned long size)
+{
+    int ret = -1;
+    char *const line = fifo_getline(fd);
+
+    if (!line)
+    {
+        fprintf(stderr, "%s: fifo_getline failed\n", __func__);
+        goto end;
+    }
+    else if (*line && (ret = process_line(line, user, thumbnail, size)))
+    {
+        if (ret < 0)
+            fprintf(stderr, "%s: process_line failed\n", __func__);
+
+        goto end;
+    }
+
+    ret = 0;
+
+end:
+    free(line);
+    return ret;
+}
+
+static volatile sig_atomic_t do_exit;
+
+static int process(const int fd, const char *const user,
+    const char *const thumbnail, const unsigned long size)
+{
+    while (!do_exit)
+    {
+        struct pollfd fds =
+        {
+            .fd = fd,
+            .events = POLLIN
+        };
+
+        int ret, res;
+
+again:
+        res = poll(&fds, 1, -1);
+
+        if (res < 0)
+        {
+            switch (errno)
+            {
+                case EAGAIN:
+                    /* Fall through. */
+                case EINTR:
+                    if (do_exit)
+                        goto end;
+
+                    goto again;
+
+                default:
+                    fprintf(stderr, "%s: poll(2): %s\n",
+                        __func__, strerror(errno));
+                    return -1;
+            }
+        }
+        else if (!res)
+        {
+            fprintf(stderr, "%s: poll(2) returned zero\n", __func__);
+            return -1;
+        }
+        else if (fds.revents & POLLHUP)
+        {
+            printf("FIFO closed by external process\n");
+            break;
+        }
+        else if ((ret = process_input(fd, user, thumbnail, size)) < 0)
+        {
+            fprintf(stderr, "%s: process_input failed\n", __func__);
+            return ret;
+        }
+    }
+
+end:
+    printf("Exiting...\n");
+    return 0;
+}
+
+struct args
+{
+    const char *user, *thumbnail;
+    unsigned long size;
+    bool force;
+};
+
+static int do_generate(const char *fpath,
+    const struct stat *sb, bool *done, void *user)
+{
+    int ret = -1;
+    const struct args *const a = user;
+    const char *const relpath = fpath + strlen(a->user);
+    bool generate = false;
+    struct dynstr d;
+    struct stat tsb;
+
+    dynstr_init(&d);
+
+    if (do_exit)
+        *done = true;
+    else if (!S_ISREG(sb->st_mode) || !extension_allowed(fpath))
+        ;
+    else if (dynstr_append(&d, "%s%s", a->thumbnail, relpath))
+    {
+        fprintf(stderr, "%s: dynstr_append failed\n", __func__);
+        goto end;
+    }
+    else if (stat(d.str, &tsb))
+    {
+        if (errno != ENOENT && errno != ENOTDIR)
+        {
+            fprintf(stderr, "%s: stat(2) %s: %s\n",
+                __func__, d.str, strerror(errno));
+            goto end;
+        }
+        else
+            generate = true;
+    }
+    else if (a->force)
+        generate = true;
+
+    if (generate)
+    {
+        if (ensure_dirs(d.str))
+        {
+            fprintf(stderr, "%s: ensure_dirs failed\n", __func__);
+            goto end;
+        }
+        else if ((ret = create_thumbnail(fpath, d.str, a->size)) < 0)
+        {
+            fprintf(stderr, "%s: create_thumbnail faled\n", __func__);
+            goto end;
+        }
+    }
+
+    ret = 0;
+
+end:
+    dynstr_free(&d);
+    return ret;
+}
+
+static int generate_existing(const char *const user,
+    const char *const thumbnail, const unsigned long size, const bool force)
+{
+    struct args a =
+    {
+        .user = user,
+        .thumbnail = thumbnail,
+        .size = size,
+        .force = force
+    };
+
+    printf("Scanning existing files...\n");
+
+    if (cftw(user, do_generate, &a))
+    {
+        fprintf(stderr, "%s: cftw failed\n", __func__);
+        return -1;
+    }
+
+    printf("Finished scanning\n");
+    return 0;
+}
+
+static void handle_signal(const int signum)
+{
+    switch (signum)
+    {
+        case SIGINT:
+            /* Fall through. */
+        case SIGTERM:
+            do_exit = 1;
+            break;
+
+        default:
+            break;
+    }
+}
+
+static int init_signals(void)
+{
+    struct sigaction sa =
+    {
+        .sa_handler = handle_signal,
+        .sa_flags = SA_RESTART
+    };
+
+    sigemptyset(&sa.sa_mask);
+
+    if (sigaction(SIGINT, &sa, NULL))
+    {
+        fprintf(stderr, "%s: sigaction(2) SIGINT: %s\n",
+            __func__, strerror(errno));
+        return -1;
+    }
+    else if (sigaction(SIGTERM, &sa, NULL))
+    {
+        fprintf(stderr, "%s: sigaction(2) SIGTERM: %s\n",
+            __func__, strerror(errno));
+        return -1;
+    }
+    else if (sigaction(SIGPIPE, &sa, NULL))
+    {
+        fprintf(stderr, "%s: sigaction(2) SIGPIPE: %s\n",
+            __func__, strerror(errno));
+        return -1;
+    }
+
+    return 0;
+}
+
+static void usage(char *const argv[])
+{
+    fprintf(stderr, "%s [-f] [-s size] dir\n", *argv);
+}
+
+static int parse_args(const int argc, char *const argv[],
+    const char **const dir, unsigned long *const size, bool *const force)
+{
+    int opt;
+
+    /* Default values. */
+    *size = 96;
+    *force = false;
+
+    while ((opt = getopt(argc, argv, "fs:")) != -1)
+    {
+        switch (opt)
+        {
+            case 'f':
+                *force = true;
+                break;
+
+            case 's':
+            {
+                char *endptr;
+
+                *size = strtoul(optarg, &endptr, 10);
+
+                if (*endptr)
+                {
+                    fprintf(stderr, "%s: invalid size %s\n", __func__, optarg);
+                    return -1;
+                }
+            }
+                break;
+
+            default:
+                usage(argv);
+                return -1;
+        }
+    }
+
+    if (optind >= argc)
+    {
+        usage(argv);
+        return -1;
+    }
+
+    *dir = argv[optind];
+    return 0;
+}
+
+int main(int argc, char *argv[])
+{
+    int ret = EXIT_FAILURE, fd = - 1;
+    char *rpath = NULL;
+    struct dynstr fifo, thumbnail, user;
+    const char *dir;
+    unsigned long size;
+    bool force;
+
+    MagickCoreGenesis(*argv, MagickTrue);
+    dynstr_init(&fifo);
+    dynstr_init(&thumbnail);
+    dynstr_init(&user);
+
+    if (parse_args(argc, argv, &dir, &size, &force))
+    {
+        usage(argv);
+        goto end;
+    }
+    else if (init_signals())
+    {
+        fprintf(stderr, "%s: init_signals failed\n", __func__);
+        goto end;
+    }
+    else if (!(rpath = crealpath(dir)))
+    {
+        fprintf(stderr, "%s: realpath(3): %s\n", __func__, strerror(errno));
+        goto end;
+    }
+    else if (dynstr_append(&thumbnail, "%s/thumbnails", rpath))
+    {
+        fprintf(stderr, "%s: dynstr_append thumbnail failed\n", __func__);
+        goto end;
+    }
+    else if (dynstr_append(&user, "%s/user", rpath))
+    {
+        fprintf(stderr, "%s: dynstr_append user failed\n", __func__);
+        goto end;
+    }
+    else if (dynstr_append(&fifo, "%s/slcl.fifo", rpath))
+    {
+        fprintf(stderr, "%s: dynstr_append fifo failed\n", __func__);
+        goto end;
+    }
+    else if ((fd = open(fifo.str, O_RDONLY | O_NONBLOCK)) < 0)
+    {
+        fprintf(stderr, "%s: open(2) %s: %s\n",
+            __func__, fifo.str, strerror(errno));
+        goto end;
+    }
+    else if (generate_existing(user.str, thumbnail.str, size, force))
+    {
+        fprintf(stderr, "%s: force_generate failed\n", __func__);
+        goto end;
+    }
+    else if (process(fd, user.str, thumbnail.str, size))
+    {
+        fprintf(stderr, "%s: process failed\n", __func__);
+        goto end;
+    }
+
+    ret = EXIT_SUCCESS;
+
+end:
+    free(rpath);
+    dynstr_free(&fifo);
+    dynstr_free(&thumbnail);
+    dynstr_free(&user);
+
+    if (fd >= 0 && close(fd))
+    {
+        fprintf(stderr, "%s: close(2): %s\n", __func__, strerror(errno));
+        ret = EXIT_FAILURE;
+    }
+
+    MagickCoreTerminus();
+    return ret;
+}