SDP(3)

✨ SDP(3) — Bluetooth SDP routines ✨

Okay bestie, welcome to SDP(3) from the Library Functions Manual 💖 This is the whole glow-up guide to the Bluetooth Service Discovery Protocol User Library, and we are gonna go through every single detail together. No cap. 🫶

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✨ NAME ✨

SDP_GET8, SDP_GET16, SDP_GET32, SDP_GET64, SDP_GET128, SDP_GET_UUID128, SDP_PUT8, SDP_PUT16, SDP_PUT32, SDP_PUT64, SDP_PUT128, SDP_PUT_UUID128, sdp_open, sdp_open_local, sdp_close, sdp_error, sdp_get_lcaddr, sdp_search, sdp_attr2desc, sdp_uuid2desc — Bluetooth SDP routines 💅

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🎀 LIBRARY 🎀

Bluetooth Service Discovery Protocol User Library — that's libsdp, and you link it with -lsdp ✨

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🦋 SYNOPSIS 🦋

#include <bluetooth.h>
#include <sdp.h>

SDP_GET8(b, cp);

SDP_GET16(s, cp);

SDP_GET32(l, cp);

SDP_GET64(l, cp);

SDP_GET128(l, cp);

SDP_GET_UUID128(l, cp);

SDP_PUT8(b, cp);

SDP_PUT16(s, cp);

SDP_PUT32(l, cp);

SDP_PUT64(l, cp);

SDP_PUT128(l, cp);

SDP_PUT_UUID128(l, cp);

void *
sdp_open(bdaddr_t const *l, bdaddr_t const *r);

void *
sdp_open_local(char const *control);

int32_t
sdp_close(void *xs);

int32_t
sdp_error(void *xs);

int32_t
sdp_get_lcaddr(void *xs, bdaddr_t *l);

int32_t
sdp_search(void *xs, uint32_t plen, uint16_t const *pp, uint32_t alen,
    uint32_t const *ap, uint32_t vlen, sdp_attr_t *vp);

char const * const
sdp_attr2desc(uint16_t attr);

char const * const
sdp_uuid2desc(uint16_t uuid);

int32_t
sdp_register_service(void *xss, uint16_t uuid, const bdaddr_t *bdaddr,
    uint8_t const *data, uint32_t datalen, uint32_t *handle);

int32_t
sdp_unregister_service(void *xss, uint32_t handle);

int32_t
sdp_change_service(void *xss, uint32_t handle, uint8_t const *data,
    uint32_t datalen);

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🌸 DESCRIPTION 🌸

Bestie, here's the tea on the macro squad ☕️

• The SDP_GET8(), SDP_GET16(), SDP_GET32(), SDP_GET64() and SDP_GET128() macros are used to get a byte, short, long, long long and 128-bit integer from the buffer pointed to by the cp pointer. The pointer is automatically advanced, like it's got main character energy and refuses to stay still 🏃‍♀️💨
• The SDP_PUT8(), SDP_PUT16(), SDP_PUT32(), SDP_PUT64() and SDP_PUT128() macros are used to put a byte, short, long, long long and 128-bit integer into the buffer pointed to by the cp pointer. The pointer is automatically advanced. Slay, honestly ✨
• The SDP_GET_UUID128() and SDP_PUT_UUID128() macros are used to get and put a 128-bit UUID into the buffer pointed to by the cp pointer. The pointer is automatically advanced. Obsessed with the consistency 💅

Now for the session functions 🫶

The sdp_open() and sdp_open_local() functions each return a pointer to an opaque object describing an SDP session. The l argument passed to sdp_open() should point to a source BD_ADDR. If the source BD_ADDR is NULL, then source address NG_HCI_BDADDR_ANY is used. The r argument passed to sdp_open() should point to a non-NULL remote BD_ADDR. Remote BD_ADDR cannot be NG_HCI_BDADDR_ANY — that's a hard no, bestie 🚫

The sdp_open_local() function takes a path to the control socket and opens a connection to a local SDP server. If the path to the control socket is NULL, then the default /var/run/sdp path will be used. Cute and convenient 🎀

The sdp_close() function terminates the active SDP session and deletes the SDP session object. The xs parameter should point to a valid SDP session object created with sdp_open() or sdp_open_local().

The sdp_error() function returns the last error that is stored inside the SDP session object. The xs parameter should point to a valid SDP session object created with sdp_open() or sdp_open_local(). The error value returned can be converted to a human readable message by calling the strerror(3) function. Very demure, very helpful 💖

The sdp_get_lcaddr() function returns the SDP session actual source BD_ADDR. The xs parameter should point to a valid SDP session object created with sdp_open(). The l parameter should point to a buffer in which the value for the requested BD_ADDR is to be returned. sdp_get_lcaddr() is useful if the current SDP session has been opened with the NG_HCI_BDADDR_ANY value passed as a source address. It's giving "wait, who am I actually?" energy 😭

The sdp_search() function is used to perform an SDP Service Search Attribute Request. The xs parameter should point to a valid SDP session object created with sdp_open() or sdp_open_local(). The pp parameter is a Service Search Pattern — an array of one or more Service Class IDs. The maximum number of Service Class IDs in the array is 12. The plen parameter is the length of the Service Search pattern.

The ap parameter is an Attribute ID Range List — an array of one or more SDP Attribute ID Range. Each attribute ID Range is encoded as a 32-bit unsigned integer data element, where the high order 16 bits are interpreted as the beginning attribute ID of the range and the low order 16 bits are interpreted as the ending attribute ID of the range. The attribute IDs contained in the Attribute ID Ranges List must be listed in ascending order without duplication of any attribute ID values. Note that all attributes may be requested by specifying a range of 0x0000-0xFFFF. The alen parameter is the length of the Attribute ID Ranges List. The SDP_ATTR_RANGE(lo, hi) macro can be used to prepare an Attribute ID Range. So handy, fr fr 🧚

The vp parameter should be an array of sdp_attr_t structures. Each sdp_attr_t structure describes a single SDP attribute and is defined as follows:

struct sdp_attr {
        uint16_t        flags;
#define SDP_ATTR_OK             (0 << 0)
#define SDP_ATTR_INVALID        (1 << 0)
#define SDP_ATTR_TRUNCATED      (1 << 1)
        uint16_t        attr;  /* SDP_ATTR_xxx */
        uint32_t        vlen;  /* length of the value[] in bytes */
        uint8_t        *value; /* base pointer */
};
typedef struct sdp_attr         sdp_attr_t;
typedef struct sdp_attr *       sdp_attr_p;

The caller of the sdp_search() function is expected to prepare the array of sdp_attr structures and for each element of the array both vlen and value must be set. The sdp_search() function will fill each sdp_attr_t structure with attribute and value, i.e., it will set flags, attr and vlen fields. The actual value of the attribute will be copied into the value buffer. 💖

Note: attributes are returned in the order they appear in the Service Search Attribute Response. SDP server could return several attributes for the same record. In this case the order of the attributes will be: all attributes for the first records, then all attributes for the second record etc. ✨

The sdp_attr2desc() and sdp_uuid2desc() functions each take a numeric attribute ID/UUID value and convert it to a human readable description. Iconic translator behavior, honestly 👑

The sdp_register_service() function is used to register a service with the local SDP server. The xss parameter should point to a valid SDP session object obtained from sdp_open_local(). The uuid parameter is a SDP Service Class ID for the service to be registered. The bdaddr parameter should point to a valid BD_ADDR. The service will be only advertised if the request was received by the local device with bdaddr. If bdaddr is set to NG_HCI_BDADDR_ANY, then the service will be advertised to any remote devices that query for it. The data and datalen parameters specify data and size of the data for the service. Upon successful return sdp_register_service() will populate handle with the SDP record handle. This parameter is optional and can be set to NULL. We love optional drama 💅

The sdp_unregister_service() function is used to unregister a service with the local SDP server. The xss parameter should point to a valid SDP session object obtained from sdp_open_local(). The handle parameter should contain a valid SDP record handle of the service to be unregistered.

The sdp_change_service() function is used to change data associated with the existing service on the local SDP server. The xss parameter should point to a valid SDP session object obtained from sdp_open_local(). The handle parameter should contain a valid SDP record handle of the service to be changed. The data and datalen parameters specify data and size of the data for the service.

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💀 CAVEAT 💀

When registering services with the local SDP server, the application must keep the SDP session open. If the SDP session is closed, then the local SDP server will remove all services that were registered over the session. The application is allowed to change or unregister a service if it was registered over the same session. This is not a drill, bestie — keep that session alive 😭🔥

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🌈 EXAMPLES 🌈

The following example shows how to get the SDP_ATTR_PROTOCOL_DESCRIPTOR_LIST attribute for the SDP_SERVICE_CLASS_SERIAL_PORT service from the remote device.

bdaddr_t       remote;
uint8_t        buffer[1024];
void          *ss    = NULL;
uint16_t       serv  = SDP_SERVICE_CLASS_SERIAL_PORT;
uint32_t       attr  = SDP_ATTR_RANGE(
                            SDP_ATTR_PROTOCOL_DESCRIPTOR_LIST,
                            SDP_ATTR_PROTOCOL_DESCRIPTOR_LIST);
sdp_attr_t     proto = { SDP_ATTR_INVALID,0,sizeof(buffer),buffer };

/* Obtain/set remote BDADDR here */

if ((ss = sdp_open(NG_HCI_BDADDR_ANY, remote)) == NULL)
        /* exit ENOMEM */
if (sdp_error(ss) != 0)
        /* exit sdp_error(ss) */

if (sdp_search(ss, 1, &serv, 1, &attr, 1, &proto) != 0)
        /* exit sdp_error(ss) */

if (proto.flags != SDP_ATTR_OK)
        /* exit see proto.flags for details */

/* If we got here then we have attribute value in proto.value */

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🩺 DIAGNOSTICS 🩺

Both sdp_open() and sdp_open_local() will return NULL if memory allocation for the new SDP session object fails. If the new SDP object was created, then the caller is still expected to call sdp_error() to check if there was a connection error. Not me being extra careful — it's literally required 😌

The sdp_get_lcaddr(), sdp_search(), sdp_register_service(), sdp_unregister_service(), and sdp_change_service() functions return a non-zero value on error. The caller is expected to call sdp_error() to find out more about the error. So if something smells off, go ask sdp_error() for the gossip 🕵️‍♀️

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👀 SEE ALSO 👀

• bluetooth(3)
• strerror(3)
• sdpcontrol(8)
• sdpd(8)

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🫶 AUTHORS 🫶

Maksim Yevmenkin <m_evmenkin@yahoo.com>

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🐛 BUGS 🐛

Most likely. Please report bugs if found. Periodt. 💀

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💖 That's the whole SDP(3) page, bestie — source/version: Debian, dated September 16, 2025. Now go slay those Bluetooth sessions! 💖