/*
    hfile_s3_write.c - Code to handle multipart uploading to S3.

    Copyright (C) 2019 Genome Research Ltd.

    Author: Andrew Whitwham <aw7@sanger.ac.uk>

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE


S3 Multipart Upload
-------------------

There are several steps in the Mulitipart upload.


1) Initiate Upload
------------------

Initiate the upload and get an upload ID.  This ID is used in all other steps.


2) Upload Part
--------------

Upload a part of the data.  5Mb minimum part size (except for the last part).
Each part is numbered and a successful upload returns an Etag header value that
needs to used for the completion step.

Step repeated till all data is uploaded.


3) Completion
-------------

Complete the upload by sending all the part numbers along with their associated
Etag values.


Optional - Abort
----------------

If something goes wrong this instructs the server to delete all the partial
uploads and abandon the upload process.


Andrew Whitwham, January 2019
*/

#define HTS_BUILDING_LIBRARY // Enables HTSLIB_EXPORT, see htslib/hts_defs.h
#include <config.h>

#include <stdarg.h>
#include <stdlib.h>
#include <string.h>
#ifdef __MSYS__
#include <strings.h>
#endif
#include <errno.h>
#include <pthread.h>

#include "hfile_internal.h"
#ifdef ENABLE_PLUGINS
#include "version.h"
#endif
#include "htslib/hts.h"
#include "htslib/kstring.h"
#include "htslib/khash.h"

#include <curl/curl.h>

#define MINIMUM_S3_WRITE_SIZE 5242880
#define S3_MOVED_PERMANENTLY 301
#define S3_BAD_REQUEST 400

// Lets the part memory size grow to about 1Gb giving a 2.5Tb max file size.
// Max. parts allowed by AWS is 10000, so use ceil(10000.0/9.0)
#define EXPAND_ON 1112

static struct {
    kstring_t useragent;
    CURLSH *share;
    pthread_mutex_t share_lock;
} curl = { { 0, 0, NULL }, NULL, PTHREAD_MUTEX_INITIALIZER };

static void share_lock(CURL *handle, curl_lock_data data,
                       curl_lock_access access, void *userptr) {
    pthread_mutex_lock(&curl.share_lock);
}

static void share_unlock(CURL *handle, curl_lock_data data, void *userptr) {
    pthread_mutex_unlock(&curl.share_lock);
}

typedef int (*s3_auth_callback) (void *auth_data, char *, kstring_t*, char*, kstring_t*, kstring_t*, kstring_t*, kstring_t*, int);

typedef int (*set_region_callback) (void *auth_data, kstring_t *region);

typedef struct {
    s3_auth_callback callback;
    redirect_callback redirect_callback;
    set_region_callback set_region_callback;
    void *callback_data;
} s3_authorisation;

typedef struct {
    hFILE base;
    CURL *curl;
    CURLcode ret;
    s3_authorisation *au;
    kstring_t buffer;
    kstring_t url;
    kstring_t upload_id;
    kstring_t completion_message;
    int part_no;
    int aborted;
    size_t index;
    long verbose;
    int part_size;
    int expand;
} hFILE_s3_write;


static void ksinit(kstring_t *s) {
    s->l = 0;
    s->m = 0;
    s->s = NULL;
}


static void ksfree(kstring_t *s) {
    free(s->s);
    ksinit(s);
}


static size_t response_callback(void *contents, size_t size, size_t nmemb, void *userp) {
    size_t realsize = size * nmemb;
    kstring_t *resp = (kstring_t *)userp;

    if (kputsn((const char *)contents, realsize, resp) == EOF) {
        return 0;
    }

    return realsize;
}


static int get_entry(char *in, char *start_tag, char *end_tag, kstring_t *out) {
    char *start;
    char *end;

    if (!in) {
        return EOF;
    }

    start = strstr(in, start_tag);
    if (!start) return EOF;

    start += strlen(start_tag);
    end = strstr(start, end_tag);

    if (!end) return EOF;

    return kputsn(start, end - start, out);
}


static void cleanup_local(hFILE_s3_write *fp) {
    ksfree(&fp->buffer);
    ksfree(&fp->url);
    ksfree(&fp->upload_id);
    ksfree(&fp->completion_message);
    curl_easy_cleanup(fp->curl);
    free(fp->au);

}


static void cleanup(hFILE_s3_write *fp) {
    // free up authorisation data
    fp->au->callback(fp->au->callback_data,  NULL, NULL, NULL, NULL, NULL, NULL, NULL, 0);
    cleanup_local(fp);
}


static struct curl_slist *set_html_headers(hFILE_s3_write *fp, kstring_t *auth, kstring_t *date, kstring_t *content, kstring_t *token) {
    struct curl_slist *headers = NULL;

    headers = curl_slist_append(headers, "Content-Type:"); // get rid of this
    headers = curl_slist_append(headers, "Expect:");       // and this
    headers = curl_slist_append(headers, auth->s);
    headers = curl_slist_append(headers, date->s);
    headers = curl_slist_append(headers, content->s);

    if (token->l) {
        headers = curl_slist_append(headers, token->s);
    }

    curl_easy_setopt(fp->curl, CURLOPT_HTTPHEADER, headers);

    return headers;
}


/*
    The partially uploaded file will hang around unless the delete command is sent.
*/
static int abort_upload(hFILE_s3_write *fp) {
    kstring_t content_hash = {0, 0, NULL};
    kstring_t authorisation = {0, 0, NULL};
    kstring_t url = {0, 0, NULL};
    kstring_t content = {0, 0, NULL};
    kstring_t canonical_query_string = {0, 0, NULL};
    kstring_t date = {0, 0, NULL};
    kstring_t token = {0, 0, NULL};
    int ret = -1;
    struct curl_slist *headers = NULL;
    char http_request[] = "DELETE";

    if (ksprintf(&canonical_query_string, "uploadId=%s", fp->upload_id.s) < 0) {
        goto out;
    }

    if (fp->au->callback(fp->au->callback_data,  http_request, NULL,
                         canonical_query_string.s, &content_hash,
                         &authorisation, &date, &token, 0) != 0) {
        goto out;
    }

    if (ksprintf(&url, "%s?%s", fp->url.s, canonical_query_string.s) < 0) {
        goto out;
    }

    if (ksprintf(&content, "x-amz-content-sha256: %s", content_hash.s) < 0) {
        goto out;
    }

    curl_easy_reset(fp->curl);
    curl_easy_setopt(fp->curl, CURLOPT_CUSTOMREQUEST, http_request);
    curl_easy_setopt(fp->curl, CURLOPT_USERAGENT, curl.useragent.s);
    curl_easy_setopt(fp->curl, CURLOPT_URL, url.s);

    curl_easy_setopt(fp->curl, CURLOPT_VERBOSE, fp->verbose);

    headers = set_html_headers(fp, &authorisation, &date, &content, &token);
    fp->ret = curl_easy_perform(fp->curl);

    if (fp->ret == CURLE_OK) {
        ret = 0;
    }

 out:
    ksfree(&authorisation);
    ksfree(&content);
    ksfree(&content_hash);
    ksfree(&url);
    ksfree(&date);
    ksfree(&canonical_query_string);
    ksfree(&token);
    curl_slist_free_all(headers);

    fp->aborted = 1;
    cleanup(fp);

    return ret;
}


static int complete_upload(hFILE_s3_write *fp, kstring_t *resp) {
    kstring_t content_hash = {0, 0, NULL};
    kstring_t authorisation = {0, 0, NULL};
    kstring_t url = {0, 0, NULL};
    kstring_t content = {0, 0, NULL};
    kstring_t canonical_query_string = {0, 0, NULL};
    kstring_t date = {0, 0, NULL};
    kstring_t token = {0, 0, NULL};
    int ret = -1;
    struct curl_slist *headers = NULL;
    char http_request[] = "POST";

    if (ksprintf(&canonical_query_string, "uploadId=%s", fp->upload_id.s) < 0) {
        return -1;
    }

    // finish off the completion reply
    if (kputs("</CompleteMultipartUpload>\n", &fp->completion_message) < 0) {
        goto out;
    }

    if (fp->au->callback(fp->au->callback_data,  http_request,
                         &fp->completion_message, canonical_query_string.s,
                         &content_hash, &authorisation, &date, &token, 0) != 0) {
        goto out;
    }

    if (ksprintf(&url, "%s?%s", fp->url.s, canonical_query_string.s) < 0) {
        goto out;
    }

    if (ksprintf(&content, "x-amz-content-sha256: %s", content_hash.s) < 0) {
        goto out;
    }

    curl_easy_reset(fp->curl);
    curl_easy_setopt(fp->curl, CURLOPT_POST, 1L);
    curl_easy_setopt(fp->curl, CURLOPT_POSTFIELDS, fp->completion_message.s);
    curl_easy_setopt(fp->curl, CURLOPT_POSTFIELDSIZE, (long) fp->completion_message.l);
    curl_easy_setopt(fp->curl, CURLOPT_WRITEFUNCTION, response_callback);
    curl_easy_setopt(fp->curl, CURLOPT_WRITEDATA, (void *)resp);
    curl_easy_setopt(fp->curl, CURLOPT_URL, url.s);
    curl_easy_setopt(fp->curl, CURLOPT_USERAGENT, curl.useragent.s);

    curl_easy_setopt(fp->curl, CURLOPT_VERBOSE, fp->verbose);

    headers = set_html_headers(fp, &authorisation, &date, &content, &token);
    fp->ret = curl_easy_perform(fp->curl);

    if (fp->ret == CURLE_OK) {
        ret = 0;
    }

 out:
    ksfree(&authorisation);
    ksfree(&content);
    ksfree(&content_hash);
    ksfree(&url);
    ksfree(&date);
    ksfree(&token);
    ksfree(&canonical_query_string);
    curl_slist_free_all(headers);

    return ret;
}


static size_t upload_callback(void *ptr, size_t size, size_t nmemb, void *stream) {
    size_t realsize = size * nmemb;
    hFILE_s3_write *fp = (hFILE_s3_write *)stream;
    size_t read_length;

    if (realsize > (fp->buffer.l - fp->index)) {
        read_length = fp->buffer.l - fp->index;
    } else {
        read_length = realsize;
    }

    memcpy(ptr, fp->buffer.s + fp->index, read_length);
    fp->index += read_length;

    return read_length;
}


static int upload_part(hFILE_s3_write *fp, kstring_t *resp) {
    kstring_t content_hash = {0, 0, NULL};
    kstring_t authorisation = {0, 0, NULL};
    kstring_t url = {0, 0, NULL};
    kstring_t content = {0, 0, NULL};
    kstring_t canonical_query_string = {0, 0, NULL};
    kstring_t date = {0, 0, NULL};
    kstring_t token = {0, 0, NULL};
    int ret = -1;
    struct curl_slist *headers = NULL;
    char http_request[] = "PUT";

    if (ksprintf(&canonical_query_string, "partNumber=%d&uploadId=%s", fp->part_no, fp->upload_id.s) < 0) {
        return -1;
    }

    if (fp->au->callback(fp->au->callback_data, http_request, &fp->buffer,
                         canonical_query_string.s, &content_hash,
                         &authorisation, &date, &token, 0) != 0) {
        goto out;
    }

    if (ksprintf(&url, "%s?%s", fp->url.s, canonical_query_string.s) < 0) {
        goto out;
    }

    fp->index = 0;
    if (ksprintf(&content, "x-amz-content-sha256: %s", content_hash.s) < 0) {
        goto out;
    }

    curl_easy_reset(fp->curl);

    curl_easy_setopt(fp->curl, CURLOPT_UPLOAD, 1L);
    curl_easy_setopt(fp->curl, CURLOPT_READFUNCTION, upload_callback);
    curl_easy_setopt(fp->curl, CURLOPT_READDATA, fp);
    curl_easy_setopt(fp->curl, CURLOPT_INFILESIZE_LARGE, (curl_off_t)fp->buffer.l);
    curl_easy_setopt(fp->curl, CURLOPT_HEADERFUNCTION, response_callback);
    curl_easy_setopt(fp->curl, CURLOPT_HEADERDATA, (void *)resp);
    curl_easy_setopt(fp->curl, CURLOPT_URL, url.s);
    curl_easy_setopt(fp->curl, CURLOPT_USERAGENT, curl.useragent.s);

    curl_easy_setopt(fp->curl, CURLOPT_VERBOSE, fp->verbose);

    headers = set_html_headers(fp, &authorisation, &date, &content, &token);
    fp->ret = curl_easy_perform(fp->curl);

    if (fp->ret == CURLE_OK) {
        ret = 0;
    }

 out:
    ksfree(&authorisation);
    ksfree(&content);
    ksfree(&content_hash);
    ksfree(&url);
    ksfree(&date);
    ksfree(&token);
    ksfree(&canonical_query_string);
    curl_slist_free_all(headers);

    return ret;
}


static ssize_t s3_write(hFILE *fpv, const void *bufferv, size_t nbytes) {
    hFILE_s3_write *fp = (hFILE_s3_write *)fpv;
    const char *buffer  = (const char *)bufferv;

    if (kputsn(buffer, nbytes, &fp->buffer) == EOF) {
        return -1;
    }

    if (fp->buffer.l > fp->part_size) {
        // time to write out our data
        kstring_t response = {0, 0, NULL};
        int ret;

        ret = upload_part(fp, &response);

        if (!ret) {
            long response_code;
            kstring_t etag = {0, 0, NULL};

            curl_easy_getinfo(fp->curl, CURLINFO_RESPONSE_CODE, &response_code);

            if (response_code > 200) {
                ret = -1;
            } else {
                if (get_entry(response.s, "ETag: \"", "\"", &etag) == EOF) {
                    ret = -1;
                } else {
                    ksprintf(&fp->completion_message, "\t<Part>\n\t\t<PartNumber>%d</PartNumber>\n\t\t<ETag>%s</ETag>\n\t</Part>\n",
                        fp->part_no, etag.s);

                    ksfree(&etag);
                }
            }
        }

        ksfree(&response);

        if (ret) {
            abort_upload(fp);
            return -1;
        }

        fp->part_no++;
        fp->buffer.l = 0;

        if (fp->expand && (fp->part_no % EXPAND_ON == 0)) {
            fp->part_size *= 2;
        }
    }

    return nbytes;
}


static int s3_close(hFILE *fpv) {
    hFILE_s3_write *fp = (hFILE_s3_write *)fpv;
    kstring_t response = {0, 0, NULL};
    int ret = 0;

    if (!fp->aborted) {

        if (fp->buffer.l) {
            // write the last part

            ret = upload_part(fp, &response);

            if (!ret) {
                long response_code;
                kstring_t etag = {0, 0, NULL};

                curl_easy_getinfo(fp->curl, CURLINFO_RESPONSE_CODE, &response_code);

                if (response_code > 200) {
                    ret = -1;
                } else {
                    if (get_entry(response.s, "ETag: \"", "\"", &etag) == EOF) {
                        ret = -1;
                    } else {
                        ksprintf(&fp->completion_message, "\t<Part>\n\t\t<PartNumber>%d</PartNumber>\n\t\t<ETag>%s</ETag>\n\t</Part>\n",
                            fp->part_no, etag.s);

                        ksfree(&etag);
                    }
                }
            }

            ksfree(&response);

            if (ret) {
                abort_upload(fp);
                return -1;
            }

            fp->part_no++;
        }

        if (fp->part_no > 1) {
            ret = complete_upload(fp, &response);

            if (!ret) {
                if (strstr(response.s, "CompleteMultipartUploadResult") == NULL) {
                    ret = -1;
                }
            }
        } else {
            ret = -1;
        }

        if (ret) {
            abort_upload(fp);
        } else {
            cleanup(fp);
        }
    }

    ksfree(&response);

    return ret;
}


static int redirect_endpoint(hFILE_s3_write *fp, kstring_t *head) {
    int ret = -1;

    if (fp->au->redirect_callback) {
        ret = fp->au->redirect_callback(fp->au->callback_data, 301, head, &fp->url);
    }

    return ret;
}

static int handle_bad_request(hFILE_s3_write *fp, kstring_t *resp) {
    kstring_t region = {0, 0, NULL};
    int ret = -1;

    if (fp->au->set_region_callback) {
        if (get_entry(resp->s, "<Region>", "</Region>", &region) == EOF) {
            return -1;
        }

        ret = fp->au->set_region_callback(fp->au->callback_data, &region);

        ksfree(&region);
    }

    return ret;
}

static int initialise_upload(hFILE_s3_write *fp, kstring_t *head, kstring_t *resp, int user_query) {
    kstring_t content_hash = {0, 0, NULL};
    kstring_t authorisation = {0, 0, NULL};
    kstring_t url = {0, 0, NULL};
    kstring_t content = {0, 0, NULL};
    kstring_t date = {0, 0, NULL};
    kstring_t token = {0, 0, NULL};
    int ret = -1;
    struct curl_slist *headers = NULL;
    char http_request[] = "POST";
    char delimiter = '?';

    if (user_query) {
        delimiter = '&';
    }

    if (fp->au->callback(fp->au->callback_data,  http_request, NULL, "uploads=",
                         &content_hash, &authorisation, &date, &token, user_query) != 0) {
        goto out;
    }

    if (ksprintf(&url, "%s%cuploads", fp->url.s, delimiter) < 0) {
        goto out;
    }

    if (ksprintf(&content, "x-amz-content-sha256: %s", content_hash.s) < 0) {
        goto out;
    }

    curl_easy_setopt(fp->curl, CURLOPT_URL, url.s);
    curl_easy_setopt(fp->curl, CURLOPT_POST, 1L);
    curl_easy_setopt(fp->curl, CURLOPT_POSTFIELDS, "");  // send no data
    curl_easy_setopt(fp->curl, CURLOPT_WRITEFUNCTION, response_callback);
    curl_easy_setopt(fp->curl, CURLOPT_WRITEDATA, (void *)resp);
    curl_easy_setopt(fp->curl, CURLOPT_HEADERFUNCTION, response_callback);
    curl_easy_setopt(fp->curl, CURLOPT_HEADERDATA, (void *)head);
    curl_easy_setopt(fp->curl, CURLOPT_USERAGENT, curl.useragent.s);

    curl_easy_setopt(fp->curl, CURLOPT_VERBOSE, fp->verbose);

    headers = set_html_headers(fp, &authorisation, &date, &content, &token);
    fp->ret = curl_easy_perform(fp->curl);

    if (fp->ret == CURLE_OK) {
        ret = 0;
    }

 out:
    ksfree(&authorisation);
    ksfree(&content);
    ksfree(&content_hash);
    ksfree(&url);
    ksfree(&date);
    ksfree(&token);
    curl_slist_free_all(headers);

    return ret;
}


static int get_upload_id(hFILE_s3_write *fp, kstring_t *resp) {
    int ret = 0;

    ksinit(&fp->upload_id);

    if (get_entry(resp->s, "<UploadId>", "</UploadId>", &fp->upload_id) == EOF) {
        ret = -1;
    }

    return ret;
}


static const struct hFILE_backend s3_write_backend = {
    NULL, s3_write, NULL, NULL, s3_close
};


static hFILE *s3_write_open(const char *url, s3_authorisation *auth) {
    hFILE_s3_write *fp;
    kstring_t response = {0, 0, NULL};
    kstring_t header   = {0, 0, NULL};
    int ret, has_user_query = 0;
    char *query_start;
    const char *env;


    if (!auth || !auth->callback || !auth->callback_data) {
        return NULL;
    }

    fp = (hFILE_s3_write *)hfile_init(sizeof(hFILE_s3_write), "w", 0);

    if (fp == NULL) {
        return NULL;
    }

    if ((fp->curl = curl_easy_init()) == NULL) {
        errno = ENOMEM;
        goto error;
    }

    if ((fp->au = calloc(1, sizeof(s3_authorisation))) == NULL) {
        goto error;
    }

    memcpy(fp->au, auth, sizeof(s3_authorisation));

    ksinit(&fp->buffer);
    ksinit(&fp->url);
    ksinit(&fp->completion_message);
    fp->aborted = 0;

    fp->part_size = MINIMUM_S3_WRITE_SIZE;
    fp->expand = 1;

    if ((env = getenv("HTS_S3_PART_SIZE")) != NULL) {
        int part_size = atoi(env) * 1024 * 1024;

        if (part_size > fp->part_size)
            fp->part_size = part_size;

        fp->expand = 0;
    }

    if (hts_verbose >= 8) {
        fp->verbose = 1L;
    } else {
        fp->verbose = 0L;
    }

    kputs(url + 4, &fp->url);

    if ((query_start = strchr(fp->url.s, '?'))) {
        has_user_query = 1;;
    }

    ret = initialise_upload(fp, &header, &response, has_user_query);

    if (ret == 0) {
        long response_code;

        curl_easy_getinfo(fp->curl, CURLINFO_RESPONSE_CODE, &response_code);

        if (response_code == S3_MOVED_PERMANENTLY) {
            if (redirect_endpoint(fp, &header) == 0) {
                ksfree(&response);
                ksfree(&header);

                ret = initialise_upload(fp, &header, &response, has_user_query);
            }
        } else if (response_code == S3_BAD_REQUEST) {
            if (handle_bad_request(fp, &response) == 0) {
                ksfree(&response);
                ksfree(&header);

                ret = initialise_upload(fp, &header, &response, has_user_query);
            }
        }

        ksfree(&header); // no longer needed
    }

    if (ret) goto error;

    if (get_upload_id(fp, &response)) goto error;

    // start the completion message (a formatted list of parts)
    ksinit(&fp->completion_message);

    if (kputs("<CompleteMultipartUpload>\n", &fp->completion_message) == EOF) {
        goto error;
    }

    fp->part_no = 1;

    // user query string no longer a useful part of the URL
    if (query_start)
         *query_start = '\0';

    fp->base.backend = &s3_write_backend;
    ksfree(&response);

    return &fp->base;

error:
    ksfree(&response);
    cleanup_local(fp);
    hfile_destroy((hFILE *)fp);
    return NULL;
}


static hFILE *hopen_s3_write(const char *url, const char *mode) {
    if (hts_verbose >= 1) {
        fprintf(stderr, "[E::%s] s3w:// URLs should not be used directly; use s3:// instead.\n", __func__);
    }
    return NULL;
}


static int parse_va_list(s3_authorisation *auth, va_list args) {
    const char *argtype;

    while  ((argtype = va_arg(args, const char *)) != NULL) {
        if (strcmp(argtype, "s3_auth_callback") == 0) {
            auth->callback = va_arg(args, s3_auth_callback);
        } else if (strcmp(argtype, "s3_auth_callback_data") == 0) {
            auth->callback_data = va_arg(args, void *);
        } else if (strcmp(argtype, "redirect_callback") == 0) {
            auth->redirect_callback = va_arg(args, redirect_callback);
        } else if (strcmp(argtype, "set_region_callback") == 0) {
            auth->set_region_callback = va_arg(args, set_region_callback);
        } else if (strcmp(argtype, "va_list") == 0) {
            va_list *args2 = va_arg(args, va_list *);

            if (args2) {
                if (parse_va_list(auth, *args2) < 0) return -1;
            }
        } else {
            errno = EINVAL;
            return -1;
        }
    }

    return 0;
}


static hFILE *vhopen_s3_write(const char *url, const char *mode, va_list args) {
    hFILE *fp = NULL;
    s3_authorisation auth = {NULL, NULL, NULL};

    if (parse_va_list(&auth, args) == 0) {
        fp =  s3_write_open(url, &auth);
    }

    return fp;
}


static void s3_write_exit() {
    if (curl_share_cleanup(curl.share) == CURLSHE_OK)
        curl.share = NULL;

    free(curl.useragent.s);
    curl.useragent.l = curl.useragent.m = 0; curl.useragent.s = NULL;
    curl_global_cleanup();
}


int PLUGIN_GLOBAL(hfile_plugin_init,_s3_write)(struct hFILE_plugin *self) {

    static const struct hFILE_scheme_handler handler =
        { hopen_s3_write, hfile_always_remote, "S3 Multipart Upload",
          2000 + 50, vhopen_s3_write
        };

#ifdef ENABLE_PLUGINS
    // Embed version string for examination via strings(1) or what(1)
    static const char id[] =
        "@(#)hfile_s3_write plugin (htslib)\t" HTS_VERSION_TEXT;
    const char *version = strchr(id, '\t') + 1;

    if (hts_verbose >= 9)
        fprintf(stderr, "[M::hfile_s3_write.init] version %s\n",
                version);
#else
    const char *version = hts_version();
#endif

    const curl_version_info_data *info;
    CURLcode err;
    CURLSHcode errsh;

    err = curl_global_init(CURL_GLOBAL_ALL);

    if (err != CURLE_OK) {
        // look at putting in an errno here
        return -1;
    }

    curl.share = curl_share_init();

    if (curl.share == NULL) {
        curl_global_cleanup();
        errno = EIO;
        return -1;
    }

    errsh  = curl_share_setopt(curl.share, CURLSHOPT_LOCKFUNC, share_lock);
    errsh |= curl_share_setopt(curl.share, CURLSHOPT_UNLOCKFUNC, share_unlock);
    errsh |= curl_share_setopt(curl.share, CURLSHOPT_SHARE, CURL_LOCK_DATA_DNS);

    if (errsh != 0) {
        curl_share_cleanup(curl.share);
        curl_global_cleanup();
        errno = EIO;
        return -1;
    }

    info = curl_version_info(CURLVERSION_NOW);
    ksprintf(&curl.useragent, "htslib/%s libcurl/%s", version, info->version);

    self->name = "S3 Multipart Upload";
    self->destroy = s3_write_exit;

    hfile_add_scheme_handler("s3w",       &handler);
    hfile_add_scheme_handler("s3w+http",  &handler);
    hfile_add_scheme_handler("s3w+https", &handler);

    return 0;
}